Which one gives only one monosubstitution product on chlorination?

In which of the following reactions is the product a hydrocarbon?

$CH_3Cl \to CH_4$
Above conversion can be achieved by

$RMgI$ when treated with ice-cold water liberated a gas which occupied $1.4 \text{ dm}^3/\text{g}$ at $STP$. The gas produced is further reacted with iodine in the presence of $HIO_3$ to give compound $(X)$. Compound $(X)$ in the presence of $Na$ and dry ether produced compound $(Y)$. The molar mass of compound $(Y)$ is . . . . . . $\text{g mol}^{-1}$. (Nearest integer)

Explain the difference between an alkane and an alkyl group with an example.

The product $(A)$ of the above reaction is: