The number of isomeric sodium salt that will be required to obtain neopentane is

Correct Answer: Option (b)

Neopentane (C₅H₁₂, i.e. 2,2-dimethylpropane) can be formed by Kolbe (radical) coupling of two alkyl radicals (R· + R′· → R–R′). To get a 5-carbon alkane we need two radicals whose carbon counts add to 5. That gives only two possibilities for the pair of radical sizes:

1 + 4 carbons (methyl + butyl)

2 + 3 carbons (ethyl + propyl)

Now count how many structural isomers each radical size has:

methyl (1C): 1 isomer.

ethyl (2C): 1 isomer.

propyl (3C): 2 isomers (n-propyl and isopropyl).

butyl (4C): 4 isomers (n-butyl, sec-butyl, isobutyl, tert-butyl).

Form the valid combinations that give total 5 carbons:

methyl (1) + any of the 4 butyl isomers → 4 different sodium salts.

ethyl (1) + any of the 2 propyl isomers → 2 different sodium salts.

Add them: 4 + 2 = 6 isomeric sodium salts whose Kolbe decarboxylation could produce neopentane (by appropriate cross-coupling).

So the answer is 6.