a b c d

a

$\text{Energy required to make a transition from energy state n to m is }$ $\Delta E = -13.6 z^2(\frac{1}{n^2} - \frac{1}{m^2}) = -13.6 \times 3^2(\frac{1}{2^2} - \frac{1}{\infty^2}) = 30.6 eV$