Consider the following statements:
I. Zinc metal, when treated with both HCl (aq.) and NaOH (aq.) separately, produces molecular hydrogen.
II. An aqueous copper sulphate solution cannot be kept in a zinc vessel.
III. Lemon, tamarind and tomato are natural sources of citric acid, oxalic acid and tartaric acid, respectively.
Which of the statements given above are correct?
NDA General Studies · Chemistry · 54 questions · 2017 to 2026
NDA Acids, bases and salts previous year questions with solutions
Acids, bases and salts are about one General Studies question in forty, two or three a sitting, rarely more. The questions are one-fact recall, though since 2026 definitions, statement sets and a titration numerical have appeared. Every question UPSC has set on it since 2017, solved. Grouped by the method each needs, newest first; open a question for its answer and worked solution.
10.1 Acids and bases: definitions, properties and reactions (10)10.2 Indicators and the pH scale (6)10.3 pH in everyday life; acids in foods, plants and stings (14)10.4 Common salt and the chemicals made from it (8)10.5 Water of crystallisation; calcium compounds and hard water (16)
10.1 Acids and bases: definitions, properties and reactions
1. NDA 2026 (II)
Answer and solution
Answer: (a) I and II only
Method. statements on acids and metals
I is true: Zn + 2HCl → ZnCl2 + H2 and Zn + 2NaOH → Na2ZnO2 + H2. II is true: Zn is more reactive than Cu and displaces it from CuSO4. III is false: tomato has oxalic acid and tamarind has tartaric acid (the order in the statement is wrong). So I and II only. NCERT Class 10 Science ch 2 (Acids, Bases and Salts).
2. NDA 2026 (I)
Consider the following statement:
“Acids are substances that dissociate in water to give hydrogen ions H+ (aq), and bases are substances that produce hydroxyl ions OH- (aq).”
The above statement is based on which one of the following concepts?
“Acids are substances that dissociate in water to give hydrogen ions H+ (aq), and bases are substances that produce hydroxyl ions OH- (aq).”
The above statement is based on which one of the following concepts?
Answer and solution
Answer: (c) Arrhenius concept
Method. Arrhenius concept
Acid = gives H+(aq), base = gives OH-(aq) in water: the Arrhenius definition. Bronsted-Lowry speaks of proton donors/acceptors; Lewis of electron-pair acceptors/donors. Standard result.
3. NDA 2026 (I)
Consider the following:
I. AlCl3
II. NH3
III. BF3
IV. FeCl3
How many of the above are Lewis acids?
I. AlCl3
II. NH3
III. BF3
IV. FeCl3
How many of the above are Lewis acids?
Answer and solution
Answer: (c) Three
Method. Lewis acids are electron-pair acceptors
AlCl3, BF3 and FeCl3 have vacant orbitals and accept an electron pair: Lewis acids. NH3 has a lone pair, so it is a Lewis base. Three. Standard result.
4. NDA 2023 (II)
Which one of the following acid is used by goldsmith for cleaning of gold and silver articles?
Answer and solution
Answer: (b) Nitric acid
Method. uses of nitric acid
Nitric acid is the acid goldsmiths use for cleaning/refining gold and silver articles; hydrochloric acid and phosphoric acid are not used this way. Standard result.
Dilute sulphuric acid is also used by goldsmiths as a pickle; answer (b) is the option conventionally expected.
5. NDA 2022 (II)
Which one of the following solutions is not capable of conducting electricity?
Answer and solution
Answer: (c) Sugar
Method. non-electrolyte
Sugar is a covalent compound that does not ionise in water, so its solution does not conduct. CuSO4, NaCl and NaOH give ions. NCERT Class 10 Science ch 2 (Acids, Bases and Salts) (conduction by acid, base and salt solutions).
6. NDA 2020 (I)
Which one of the following was the first mineral acid discovered?
Answer and solution
Answer: (a) Sulphuric acid
Method. history: sulphuric acid is the earliest mineral acid
Sulphuric acid (oil of vitriol, from distilling vitriol) is credited to Jabir ibn Hayyan (8th century) and Al-Razi, earlier than hydrochloric acid and nitric acid, whose clear descriptions come later (nitric acid in the Pseudo-Geber texts, about the 13th century). Standard result, not an NCERT row.
7. NDA 2019 (I)
Which one of the following is an organic acid?
Answer and solution
Answer: (c) Acetic acid
Method. acetic acid is organic
Acetic acid, CH3COOH, is a carboxylic (organic) acid; the others are mineral acids. Standard result.
8. NDA 2019 (I)
Which one of the following will NOT produce carbon dioxide on reacting with an aqueous solution of hydrochloric acid?
Answer and solution
Answer: (b) Quick Lime
Method. carbonates react with HCl to give CO2; CaO does not
Limestone, chalk and marble are CaCO3: CaCO3 + 2HCl → CaCl2 + H2O + CO2. Quick lime is CaO, an oxide: CaO + 2HCl → CaCl2 + H2O, no CO2. NCERT Class 10 Science ch 2 (Acids, Bases and Salts).
9. NDA 2018 (II)
Which one of the following is a tribasic acid?
Answer and solution
Answer: (d) Phosphoric acid
Method. basicity = replaceable H+
H3PO4 gives three H+ per molecule (tribasic). HCl and HNO3 are monobasic and H2SO4 is dibasic. Standard result.
10. NDA 2017 (II)
Which compound, when dissolved in water, conducts electricity and forms a basic solution?
Answer and solution
Answer: (d) NaOH
Method. strong base ionises fully, basic solution
NaOH is a strong base: it ionises to Na+ and OH-, conducts electricity and gives a basic solution. HCl is acidic; CH3COOH is acidic; CH3OH does not ionise. NCERT Class 10 Science ch 2 (Acids, Bases and Salts).
10.2 Indicators and the pH scale
11. NDA 2026 (II)
In a dry test tube, 2 mL of HCl (0.1 N) is taken. To this, 4 mL of NaOH (0.1 N) is added. The solution is stirred well, followed by the addition of 2 drops of phenolphthalein. What will be the colour of the solution?
Answer and solution
Answer: (c) Pink
Method. neutralisation, excess base
HCl: 2 mL × 0.1 N = 0.2 meq; NaOH: 4 mL × 0.1 N = 0.4 meq. Excess NaOH = 0.2 meq in 6 mL, [OH-] = 0.0333 M, pOH = 1.48, pH = 12.52 (basic). Phenolphthalein is pink in base. NCERT Class 10 Science ch 2 (Acids, Bases and Salts) (indicators, neutralisation).
12. NDA 2025 (I)
Which one of the following statements is NOT correct?
Answer and solution
Answer: (b) The higher the hydrogen ion concentration in a solution, higher is its pH
Method. pH and [H+] are inverse
The question is negative. pH = -log[H+], so the higher the hydrogen ion concentration, the lower the pH; statement (b) is wrong. (a), (c) and (d) are correct. NCERT Class 10 Science ch 2 (Acids, Bases and Salts) (pH scale).
13. NDA 2024 (I)
Litmus, a well-known acid-base indicator, is derived from:
Answer and solution
Answer: (b) Lichens
Method. litmus from lichens
Litmus is a natural indicator extracted from lichens. NCERT Class 10 Science ch 2 (Acids, Bases and Salts).
14. NDA 2020 (I)
Which one of the following is the correct sequence of change in colours when a turmeric stain on white clothes is scrubbed by soap and then washed with water?
Answer and solution
Answer: (b) Yellow – reddish brown – yellow
Method. turmeric is an acid-base indicator
Turmeric is yellow in neutral/acidic medium and turns reddish brown with the basic soap. Rinsing with water removes the soap and the yellow stain shows again: yellow – reddish brown – yellow. NCERT Class 10 Science ch 2 (Acids, Bases and Salts).
15. NDA 2018 (II)
The solution of which one of the following will have pH less than 7?
Answer and solution
Answer: (c) FeCl3
Method. salt of strong acid and weak base is acidic
FeCl3 is the salt of a strong acid (HCl) and a weak base (Fe(OH)3); Fe3+ hydrolyses and gives an acidic solution, pH below 7. KCl and NaCl are neutral and NaOH is basic. NCERT Class 10 Science ch 2 (Acids, Bases and Salts) (salts and pH).
16. NDA 2018 (I)
Which one of the following gives the highest amount of hydrogen ions (H+)?
Answer and solution
Answer: (d) Gastric juice
Method. lower pH = more H+
Gastric juice (HCl, pH about 1.5 to 3.5) is more acidic than lemon juice (pH about 2.2); NaOH and milk of magnesia are basic and have very few H+. Lower pH means higher [H+]: pH 1.5 gives [H+] = 10-1.5 = 0.03 M, against 10-2.2 = 0.006 M for lemon juice. NCERT Class 10 Science ch 2 (Acids, Bases and Salts) (pH of body fluids).
10.3 pH in everyday life; acids in foods, plants and stings
17. NDA 2026 (II)
Consider the following statements:
I. The leaves of nettle, a herbaceous plant, cause painful stings when touched accidentally because of the secretion of formic acid.
II. When gypsum is heated at 100°C, it forms calcium carbonate hemihydrate, called Plaster of Paris.
III. When moistened with water, anhydrous copper sulphate forms a green-coloured copper sulphate dihydrate.
Which of the statements given above is/are correct?
I. The leaves of nettle, a herbaceous plant, cause painful stings when touched accidentally because of the secretion of formic acid.
II. When gypsum is heated at 100°C, it forms calcium carbonate hemihydrate, called Plaster of Paris.
III. When moistened with water, anhydrous copper sulphate forms a green-coloured copper sulphate dihydrate.
Which of the statements given above is/are correct?
Answer and solution
Answer: (a) I only
Method. statements on nettle, PoP, CuSO4
I is true (formic acid). II as printed is false: gypsum on heating at 100 °C gives plaster of Paris, calcium sulphate hemihydrate, not calcium carbonate hemihydrate. III is false: anhydrous CuSO4 is white and turns blue with water (CuSO4·5H2O). Only I is correct. NCERT Class 10 Science ch 2 (Acids, Bases and Salts).
18. NDA 2025 (I)
For acid rain, the pH of rain water should be less than
Answer and solution
Answer: (c) 5.6
Method. acid rain threshold
Rain water is naturally slightly acidic (about pH 5.6, dissolved CO2); rain with pH below 5.6 is acid rain. Standard result.
19. NDA 2024 (I)
Human body works in the pH range of:
Answer and solution
Answer: (b) 7.0 – 7.8
Method. pH of body
NCERT: our body works within the pH range 7.0 to 7.8. NCERT Class 10 Science ch 2 (Acids, Bases and Salts).
20. NDA 2024 (I)
Which one among the following is present in the nettle leaf hairs that causes burning pain?
Answer and solution
Answer: (a) Methanoic acid
Method. nettle sting = methanoic acid
Nettle hairs inject methanoic acid. Acetic acid is the same as ethanoic acid, not the sting acid. NCERT Class 10 Science ch 2 (Acids, Bases and Salts).
21. NDA 2024 (I)
Which one among the following is known as Milk of Magnesia?
Answer and solution
Answer: (d) Magnesium hydroxide
Method. milk of magnesia = Mg(OH)2
Milk of magnesia is a suspension of magnesium hydroxide in water, used as an antacid. NCERT Class 10 Science ch 2 (Acids, Bases and Salts).
22. NDA 2023 (I)
Among the following, which is not the correct method for keeping the curd?
Answer and solution
Answer: (b) Keeping in copper vessel
Method. acids attack copper
Curd (sour, containing lactic acid) should not be kept in copper vessels because the acid reacts with copper to form poisonous copper salts; steel, plastic and glass are not attacked. NCERT Class 10 Science ch 2 (Acids, Bases and Salts) (acids with metals). Standard practical reason.
23. NDA 2023 (I)
Toothpaste prevents tooth decay by:
Answer and solution
Answer: (a) neutralizing the excess acidity.
Method. toothpaste neutralises mouth acidity
Toothpaste is basic and neutralises the acid formed by bacteria in the mouth, preventing decay of the enamel (NCERT's explanation). Fluoride also helps, but by the acid-base chemistry asked, (a). NCERT Class 10 Science ch 2 (Acids, Bases and Salts).
Option (c), the action of fluoride, is also a true commercial reason for toothpaste's decay prevention; answer follows the chemistry of neutralising acidity.
24. NDA 2022 (II)
Bee sting leaves an acid which causes pain and irritation. The acid released is
Answer and solution
Answer: (d) methanoic acid
Method. sting acid is methanoic acid
A bee (or ant) sting injects methanoic (formic) acid, HCOOH. NCERT Class 10 Science ch 2 (Acids, Bases and Salts).
25. NDA 2021 (II)
The pH value of Milk of Magnesia is approximately
Answer and solution
Answer: (c) 10
Method. milk of magnesia is mildly basic
Milk of magnesia, Mg(OH)2, is a weak base with pH about 10, used as an antacid. NCERT Class 10 Science ch 2 (Acids, Bases and Salts).
26. NDA 2021 (I)
Which one of the following acids is predominantly found in tomatoes?
Answer and solution
Answer: (c) Oxalic acid
Method. tomato contains oxalic acid
NCERT lists tomato as a source of oxalic acid (lemon: citric, tamarind: tartaric, sour milk: lactic, vinegar: acetic). NCERT Class 10 Science ch 2 (Acids, Bases and Salts).
27. NDA 2018 (I)
The accidental touch of Nettle leaves creates a burning sensation, which is due to inject of
Answer and solution
Answer: (b) Methanoic acid
Method. nettle sting = methanoic acid
Nettle hairs inject methanoic (formic) acid, HCOOH. NCERT Class 10 Science ch 2 (Acids, Bases and Salts).
28. NDA 2018 (I)
Which of the following properties is true for a tooth paste?
Answer and solution
Answer: (c) It is basic
Method. toothpaste is basic
Toothpastes are generally basic and neutralise the acid produced by bacteria in the mouth, which prevents enamel decay. Option d is not a property of toothpaste (enamel is calcium phosphate, but toothpaste is not made of it). NCERT Class 10 Science ch 2 (Acids, Bases and Salts).
29. NDA 2017 (II)
The desirable range of pH for drinking water is
Answer and solution
Answer: (a) 6.5 to 8.5
Method. BIS drinking-water pH limit
The desirable pH range for drinking water (BIS/WHO) is 6.5 to 8.5. Standard result, not an NCERT row.
30. NDA 2017 (I)
Stung by hairs of nettle leaves causes burning pain. This is due to the injection of
Answer and solution
Answer: (b) Methanoic acid
Method. nettle sting = methanoic acid
Nettle hair injects methanoic (formic) acid, HCOOH, the same acid as an ant sting. NCERT Class 10 Science ch 2 (Acids, Bases and Salts).
10.4 Common salt and the chemicals made from it
31. NDA 2025 (I)
Match List I with List II and select the answer using the code given below the Lists:
List I (Chemical Name)
A. Washing soda
B. Baking soda
C. Bleaching powder
D. Gypsum
List II (Chemical Formula)
1. CaOCl2
2. NaHCO3
3. Na2CO3·10H2O
4. CaSO4·2H2O
Code:
A B C D
List I (Chemical Name)
A. Washing soda
B. Baking soda
C. Bleaching powder
D. Gypsum
List II (Chemical Formula)
1. CaOCl2
2. NaHCO3
3. Na2CO3·10H2O
4. CaSO4·2H2O
Code:
A B C D
| (blank) | A | B | C | D |
|---|---|---|---|---|
| (a) | 4 | 2 | 1 | 3 |
| (b) | 4 | 1 | 2 | 3 |
| (c) | 3 | 1 | 2 | 4 |
| (d) | 3 | 2 | 1 | 4 (the code table of the match item |
| List I and List II printed side by side as two columns) |
Answer and solution
Answer: (d) 3 2 1 4
Method. matching names with formulas
Washing soda = Na2CO3·10H2O (3); baking soda = NaHCO3 (2); bleaching powder = CaOCl2 (1); gypsum = CaSO4·2H2O (4). Code A-3, B-2, C-1, D-4, option (d). NCERT Class 10 Science ch 2 (Acids, Bases and Salts).
32. NDA 2021 (I)
Common salt (NaCl) is not used as a raw material for preparation of which one of the following compounds?
Answer and solution
Answer: (c) Plaster of Paris
Method. NaCl chemistry
Bleaching powder (Cl2 from brine electrolysis), baking soda and washing soda (Solvay-type route from NaCl) all use common salt. Plaster of Paris comes from heating gypsum, CaSO4·2H2O, with no NaCl. NCERT Class 10 Science ch 2 (Acids, Bases and Salts).
33. NDA 2020 (I)
At nearly 70°C, sodium bicarbonate shows the property of gradually decomposing, which makes it usable in bakery products. The product of decomposition responsible for this use of sodium bicarbonate is
Answer and solution
Answer: (a) Carbon dioxide
Method. NaHCO3 on heating gives CO2
2NaHCO3 → Na2CO3 + H2O + CO2. The CO2 released makes cakes and bread rise (spongy). NCERT Class 10 Science ch 2 (Acids, Bases and Salts).
34. NDA 2018 (I)
Brine is an aqueous solution of
Answer and solution
Answer: (a) NaCl
Method. brine = sodium chloride solution
Brine is concentrated aqueous NaCl, the raw material of the chlor-alkali process. NCERT Class 10 Science ch 2 (Acids, Bases and Salts).
35. NDA 2018 (I)
Which one of the following is the chemical formula of Washing Soda?
Answer and solution
Answer: (b) Na2CO3·10H2O
Method. washing soda formula
Washing soda is Na2CO3·10H2O (sodium carbonate decahydrate). Na2CO3·5H2O is not the common form. NCERT Class 10 Science ch 2 (Acids, Bases and Salts).
36. NDA 2018 (I)
Which one of the following is NOT true for bleaching powder?
Answer and solution
Answer: (a) It is used as a reducing agent in chemical industries
Method. bleaching powder is an oxidising agent
CaOCl2 acts as an oxidising agent (it gives chlorine/hypochlorite), not a reducing agent, so (a) is not true. It is used to bleach wood pulp and linen and to disinfect drinking water. NCERT Class 10 Science ch 2 (Acids, Bases and Salts).
37. NDA 2017 (II)
Which one among the following chemicals is used as washing soda?
Answer and solution
Answer: (c) Sodium carbonate
Method. washing soda = sodium carbonate
Washing soda is Na2CO3·10H2O, sodium carbonate; sodium bicarbonate is baking soda. NCERT Class 10 Science ch 2 (Acids, Bases and Salts).
38. NDA 2017 (I)
The chemical name of baking soda is
Answer and solution
Answer: (b) NaHCO3
Method. baking soda = sodium hydrogencarbonate
Baking soda is NaHCO3; Na2CO3 is washing soda, CaCO3 is limestone, NaOH is caustic soda. NCERT Class 10 Science ch 2 (Acids, Bases and Salts).
10.5 Water of crystallisation; calcium compounds and hard water
39. NDA 2025 (II)
The reaction that occurs on passing carbon dioxide gas through lime water is
Answer and solution
Answer: (b) Ca(OH)2 + CO2 → CaCO3 + H2O
Method. lime water test
Ca(OH)2 + CO2 → CaCO3 + H2O (milky white precipitate). The reaction in (a) occurs only on passing excess CO2. NCERT Class 10 Science ch 2 (Acids, Bases and Salts).
40. NDA 2025 (II)
Which one of the following statements is NOT correct?
Answer and solution
Answer: (b) The molecular formula of Plaster of Paris is CaSO4·2H2O
Method. plaster of Paris formula
The question is negative. Plaster of Paris is CaSO4·½H2O; CaSO4·2H2O is gypsum, so (b) is not correct. (a), (c) and the Venus clouds of sulphuric acid in (d) are correct. NCERT Class 10 Science ch 2 (Acids, Bases and Salts).
41. NDA 2025 (II)
Which one of the following salts is responsible for temporary hardness of water?
Answer and solution
Answer: (c) Bicarbonates of magnesium
Method. temporary hardness
Temporary hardness is due to bicarbonates (hydrogencarbonates) of calcium and magnesium; sulphates and chlorides cause permanent hardness. Standard result.
42. NDA 2024 (I)
Which among the following is the correct composition of Borax?
Answer and solution
Answer: (b) Sodium, Boron, Oxygen and Hydrogen
Method. borax Na2B4O7·10H2O
Borax is Na2B4O7·10H2O: sodium, boron, oxygen and hydrogen. Standard result.
43. NDA 2023 (I)
Copper sulphate crystals available in the market are blue coloured crystals. By careful heating, they turn to white colour. Which one of the following is responsible for the blue colour?
Answer and solution
Answer: (c) Water
Method. water of crystallisation gives the colour
Blue CuSO4·5H2O loses its water of crystallisation on heating and becomes white anhydrous CuSO4; so water is responsible for the blue colour. NCERT Class 10 Science ch 2 (Acids, Bases and Salts).
44. NDA 2022 (II)
Which one of the following salts does not possess water of crystallization?
Answer and solution
Answer: (a) Potassium permanganate
Method. hydrated salts
Blue vitriol is CuSO4·5H2O, washing soda Na2CO3·10H2O and Mohr's salt FeSO4·(NH4)2SO4·6H2O are hydrated. KMnO4 has no water of crystallisation. Standard result.
45. NDA 2021 (II)
What is the number of water molecules present in a Ferrous Sulphate crystal?
Answer and solution
Answer: (d) 7
Method. ferrous sulphate crystal FeSO4·7H2O
Green ferrous sulphate crystals are FeSO4·7H2O, seven water molecules. NCERT Class 10 Science ch 2 (Acids, Bases and Salts).
46. NDA 2021 (II)
What is the colour of the precipitate obtained by passing CO2 gas through lime water?
Answer and solution
Answer: (c) White
Method. lime water turns milky
Ca(OH)2 + CO2 → CaCO3↓ + H2O; the precipitate of calcium carbonate is white. NCERT Class 10 Science ch 2 (Acids, Bases and Salts).
47. NDA 2021 (II)
Which one of the following is the chemical formula of Plaster of Paris?
Answer and solution
Answer: (a) CaSO4 · 12 H2O
Method. plaster of Paris is hemihydrate
Plaster of Paris is CaSO4·½H2O. NCERT Class 10 Science ch 2 (Acids, Bases and Salts).
48. NDA 2020 (I)
Chalk and marble are different forms of
Answer and solution
Answer: (b) Calcium carbonate
Method. chalk and marble = CaCO3
Chalk, marble and limestone are all forms of calcium carbonate. NCERT Class 10 Science ch 2 (Acids, Bases and Salts).
49. NDA 2020 (I)
Number of molecules of water of crystallization in copper sulphate, sodium carbonate and Gypsum are
Answer and solution
Answer: (a) 5, 10 and 2 respectively
Method. water of crystallisation
CuSO4·5H2O (5), Na2CO3·10H2O (10), gypsum CaSO4·2H2O (2): 5, 10 and 2. NCERT Class 10 Science ch 2 (Acids, Bases and Salts).
50. NDA 2019 (II)
Which one of the following does not represent the salt, Calcium carbonate?
Answer and solution
Answer: (a) Lime water
Method. lime water is Ca(OH)2
The question is negative. Limestone, chalk and marble are forms of CaCO3; lime water is calcium hydroxide, Ca(OH)2, so it does not represent calcium carbonate. NCERT Class 10 Science ch 2 (Acids, Bases and Salts).
51. NDA 2018 (II)
Permanent hardness of water cannot be removed by which one of the following methods?
Answer and solution
Answer: (c) Boiling
Method. boiling removes only temporary hardness
Boiling removes only temporary hardness (hydrogencarbonates). Permanent hardness (Ca/Mg chlorides and sulphates) is removed by washing soda, Calgon and ion exchange. Standard result.
52. NDA 2018 (II)
Which one of the following is the chemical formula of gypsum?
Answer and solution
Answer: (a) CaSO4·2H2O
Method. gypsum is calcium sulphate dihydrate
Gypsum is CaSO4·2H2O; 2CaSO4·H2O is plaster of Paris. NCERT Class 10 Science ch 2 (Acids, Bases and Salts).
53. NDA 2018 (I)
Which one of the following is the number of water molecules that share with two formula unit CaSO4 in plaster of Paris?
Answer and solution
Answer: (a) One
Method. plaster of Paris is CaSO4·½H2O
Plaster of Paris is CaSO4·½H2O, written (CaSO4)2·H2O: one water molecule is shared by two formula units of CaSO4. NCERT Class 10 Science ch 2 (Acids, Bases and Salts).
54. NDA 2017 (I)
Temporary hardness in water is due to which one of the following of Calcium and Magnesium?
Answer and solution
Answer: (a) Hydrogencarbonates
Method. temporary hardness = Ca/Mg hydrogencarbonates
Temporary hardness is due to dissolved Ca(HCO3)2 and Mg(HCO3)2; boiling decomposes them to insoluble carbonates. Carbonates are insoluble; chlorides and sulphates give permanent hardness. Standard result.
← Atomic structure, periodic table and bondingRedox, metals and non-metals →