How many compound(s) given below have chiral carbon?

The correct answer is 2.

A chiral carbon (or asymmetric carbon atom) is a carbon atom that is sp³ hybridized and is bonded to four different atoms or groups of atoms. Let us analyze each of the given compounds to identify the presence of any chiral carbons:

Compound (i): 2-methylcyclohexanone
In this cyclic compound, carbon-2 (which is attached to the methyl group, -CH₃) is bonded to:
1. A methyl group (-CH₃)
2. A hydrogen atom (-H)
3. The carbonyl group side of the ring (-C(=O)CH₂...)
4. The methylene group side of the ring (-CH₂CH₂...)
Since all four groups attached to this carbon are different, it is a chiral carbon. Thus, compound (i) contains a chiral carbon.

Compound (ii): cyclohexane-1,3-dione
In this compound, all the sp³ hybridized carbons (C-2, C-4, C-5, C-6) are symmetric. Specifically, C-2 is bonded to two hydrogen atoms, and each of C-4, C-5, and C-6 is also bonded to two hydrogen atoms (with symmetric paths in both directions along the ring). The carbonyl carbons (C-1 and C-3) are sp² hybridized and cannot be chiral. Therefore, compound (ii) does not have any chiral carbon.

Compound (iii): 3-iodopentane
The structural formula is:
CH₃-CH₂-CH(I)-CH₂-CH₃
The central carbon atom (C-3) is bonded to a hydrogen atom (-H), an iodine atom (-I), and two identical ethyl groups (-CH₂-CH₃). Because two of the attached groups are identical, C-3 is achiral. No other carbon atom in the molecule has four different groups. Therefore, compound (iii) does not have a chiral carbon.

Compound (iv): 2-hydroxybutanoic acid
The structural formula is:
CH₃-CH₂-CH(OH)-COOH
The second carbon (C-2) is bonded to:
1. A hydrogen atom (-H)
2. A hydroxyl group (-OH)
3. An ethyl group (-CH₂-CH₃)
4. A carboxylic acid group (-COOH)
Since this carbon is bonded to four distinct groups, it is a chiral carbon. Thus, compound (iv) contains a chiral carbon.

Comparing all four compounds, only compound (i) and compound (iv) contain a chiral carbon. Therefore, there are exactly 2 compounds with a chiral carbon.