Class 11 Chemistry Chapter 1: Some Basic Concepts of Chemistry MCQs with answers
10 multiple-choice questions on Some Basic Concepts of Chemistry, each with its answer and the reason, written from the NCERT chapter. For school exams on the CBSE pattern, JEE Main and NEET, which are set from the same NCERT chapter. Open a question's solution to check your working; then take the free test to find your next chapter.
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Answer: (d) molarity
Molarity is moles per litre of solution, and the volume of a solution changes with temperature. Molality, mass per cent and mole fraction depend only on masses or moles, which do not change on warming.
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Answer: (b) air
Air is a mixture whose components are uniformly distributed, so its composition is the same throughout. Salt with sugar, and grains with dirt, are heterogeneous; glucose is a pure substance (a compound).
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Answer: (c) whether it burns in air to form magnesium oxide
Combustibility is a chemical property: observing it needs the magnesium to change into a new substance, magnesium oxide. Colour, density and melting point are physical properties, measured without changing the identity of the metal.
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Answer: (a) 450 pm
1 nm = 10⁻⁹ m and 1 pm = 10⁻¹² m, so 0.45 nm × (10⁻⁹ m / 1 nm) × (1 pm / 10⁻¹² m) = 0.45 × 10³ pm = 450 pm.
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Answer: (a) 77.15 K
K = °C + 273.15 = −196 + 273.15 = 77.15 K. A negative value is not possible on the Kelvin scale; 469.15 comes from subtracting instead of adding.
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Answer: (c) −40°
Put °F = °C = x in °F = (9/5)(°C) + 32: x = 9x/5 + 32, so −4x/5 = 32 and x = −40. So −40 °C = −40 °F.
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Answer: (b) 20.60 g
In 0.02060 the leading zeros are not significant, the zero between 2 and 6 is, and the terminal zero after the decimal point is: four figures (2, 0, 6, 0). 20.60 also has four. 2060 (no decimal point) has three, and 2.06 and 0.206 have three.
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Answer: (d) 16.4 g
The sum is 16.423 g. In addition the result may carry no more decimal places than the least precise figure, 4.2 g (one decimal place), so it is reported as 16.4 g.
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Answer: (c) 2.7 g mL⁻¹
Density = mass/volume = 12.5 g / 4.6 mL = 2.717... g mL⁻¹. In division the result keeps the significant figures of the least precise measurement: 4.6 has two, so the density is 2.7 g mL⁻¹.
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Answer: (a) 4.725 → 4.72 and 3.635 → 3.64
When the digit removed is 5, the preceding digit is left unchanged if it is even and raised by one if it is odd. In 4.725 the preceding digit 2 is even, giving 4.72; in 3.635 the preceding digit 3 is odd, giving 3.64.