a b c d

b

$\text{Velocity of electron in an orbit is inversely propotional to n}$ $ V \propto \frac{1}{n}$ $ \frac{\lambda_B}{\lambda_G} = \frac{V_G}{V_B} = \frac{n_B}{n_G}= 3:1$ $ \lambda_B = 3 \lambda_G$