$N$ moles of diatomic gas in a cylinder is at a temperature $T$. Heat is supplied to the cylinder such that the temperature remains constant but $n$ moles of the diatomic gas get converted into monoatomic gas. The change in the total kinetic energy of the gas is\\
(1) 0\\
(2) $\frac { 5 } { 2 } n R T$\\
(3) $\frac { 3 } { 2 } n R T$\\
(4) $\frac { 1 } { 2 } n R T$