Class 11 Chemistry Chapter 8: Organic Chemistry – Some Basic Principles and Techniques MCQs with answers
10 multiple-choice questions on Organic Chemistry – Some Basic Principles and Techniques, 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.
Show answer
Answer: (c) ammonium cyanate
Wöhler heated ammonium cyanate: NH₄CNO → NH₂CONH₂. The other three are inorganic salts, but not the one he used.
Show answer
Answer: (a) CH₂=CH–CH=CH₂
Each carbon of CH₂=CH–CH=CH₂ forms one double bond, so all four are sp². In CH₂=C=CH₂ the middle carbon (two double bonds) is sp and the ends sp²; CH₃–C≡CH has sp³ and sp; CH₂=CH–C≡N has sp² and sp.
Show answer
Answer: (b) 7 σ and 2 π
σ bonds: C=C (1), C–C (1), C=O (1) and four C–H, total 7. π bonds: one in C=C and one in C=O, total 2. 6 σ forgets the aldehyde C–H; 3 π counts the C–C single bond as a π bond.
Show answer
Answer: (d) 53.3%
Each mole of O₂ in the compound gives 2 mol CO₂, so 88 g CO₂ comes from 32 g O₂. % O = (32 × 0.44 × 100)/(88 × 0.30) = 53.3%. Using 44 g gives an impossible 106.7%; 40.0% is the carbon fraction 12/44; 26.7% halves the right answer.
Show answer
Answer: (a) HC≡CH
Electronegativity of carbon rises with the s character of its hybrid orbitals. The sp carbon of ethyne has 50% s character, more than sp² (33%) or sp³ (25%).
Show answer
Answer: (d) pentan-2-one
Four segments have five points, each a carbon; the ends are CH₃ groups. The C=O on the second carbon makes it CH₃COCH₂CH₂CH₃, pentan-2-one. Butan-2-one counts segments instead of points; pentanal would need the O at an end.
Show answer
Answer: (b) projects out of the plane of the paper, towards the observer
A solid wedge points towards the observer, its broad end nearer; a dashed wedge points away; a plain line lies in the plane.
Show answer
Answer: (c) space-filling model
The space-filling model shows the relative size of each atom from its van der Waals radius and no bonds. The framework model shows only bonds; ball-and-stick and ball-and-spring show both atoms and bonds.
Show answer
Answer: (d) a heterocyclic alicyclic (non-aromatic) compound
Its ring holds an atom other than carbon, so it is heterocyclic, and it is saturated, so it is alicyclic, not aromatic. Furan, its unsaturated relative, is the heterocyclic aromatic one.
Show answer
Answer: (a) 4-ethyl-2-methylhexane
The longest chain has six carbons. Numbering from the left puts the branches at 2 and 4 (from the right, 3 and 5), so 2 and 4. Ethyl is written before methyl in alphabetical order: 4-ethyl-2-methylhexane. Option c breaks the alphabetical order; option d does not use the longest chain.