Given below are four compounds :
(a) n-propyl chloride
(b) iso-propyl chloride
(c) sec-butyl chloride
(d) neo-pentyl chloride
Percentage of carbon in the one which exhibits optical isomerism is :

Optical isomerism occurs when a compound has a chiral center (asymmetric carbon).
Examining each compound:
n-propyl chloride (CH3CH2CH2Cl) has no chiral center,
iso-propyl chloride (CH3CHClCH3) has no chiral center,
sec-butyl chloride (CH3CH2CHClCH3) has one chiral center attached to four different groups, and
neo-pentyl chloride has no chiral center.

Therefore, sec-butyl chloride exhibits optical isomerism.

For C4H9Cl:
molar mass = 4(12) + 9(1) + 35.5 = 92.5 g/mol.
Carbon percentage = (48/92.5) × 100 = 51.89% ≈ 52%