An isomer of C6H14 forms three monochloro derivatives. The isomer may be -(Excluding stereo isomer)neo-pentanen-hexane2, 3-dimethylbutaneiso-hexane

The isomer of C6H14 that forms three monochloro derivatives is 2,3-dimethylbutane.

Here's why:

1. Draw the structure of 2,3-dimethylbutane. It has a four-carbon chain with two methyl groups attached to the second and third carbons.

2. Identify the hydrogens that could be replaced by chlorine to form a monochloro derivative. There are three types of hydrogens: those on the end carbons of the main chain, those on the second and third carbons of the main chain, and those on the methyl groups.

3. Each of these types of hydrogens will give a different monochloro derivative when replaced by chlorine. Therefore, 2,3-dimethylbutane can form three monochloro derivatives.

The other isomers of C6H14 (n-hexane, iso-hexane, and neo-pentane) can form more than three monochloro derivatives, so they are not the correct answer.