(c)
Higher the value of $(n + l)$, higher will be the energy of electrons. If value of $(n + l)$ is same for any two or more electrons, the electron with higher value of $n$, has higher energy. Hence, the correct order of energy is
$V < I < III < II < IV$
$\because\ \ \ (n + 1)$ 4 5 5 5 6