When a metallic surface is illuminated with radiation of wavelength $\lambda$, the stopping potential is $V$. If the same surface is illuminated with radiation of wavelength $2 \lambda$, the stopping potential is $\frac{V}{4}$. The threshold wavelength for the metallic surface is :

Question

( A ) $ 5 \lambda$
( B ) $ 3 \lambda$
( C ) $ \frac{5}{2} \lambda$
( D ) $ 4 \lambda$