Monochromatic radiation emitted when electron on hydrogen atom jumps from first excited to the ground state irradiates a photosensitive material. The stopping potential is measured to be 3.57 V. The threshold frequency of the material is

Question

( A ) $4.\times 10^{15}$ Hz
( B ) $5 \times 10^{15}$ Hz
( C ) $1.6\times 10^{15} Hz$
( D ) $2.5 \times10^{15}$ Hz