When transition is from upper state to lower state, the energy is evolved. Therefore, options (C) and (d) are practicable.

In option (C)

$E=-Rhc \left[\frac{1}{1^2}-\frac{1}{2^2}\right]=-\frac{3}{4}Rhc$

In option (d)

$E=-Rhc \left(\frac{1}{2^2}-\frac{1}{6^2}\right)$

$=-\frac{2}{9}Rhc$

Thus, maximum energy is evolved in option (c).