The lower stability of ethyl anion $\left(C{H}_{3}C{H_2}^{-}\right)$ Compared to methyl anion $\left(C{H}_3^{-}\right)$ is because of $+I$ -effect of methyl group of ethyl anion. The higher stability of ethyl radical compared to methyl radical is due to $\sigma -p$ -orbital conjugation which is known as hyper conjugation in ethyl radical.