Correct option is C. $$1.66\ eV$$
$$hv = \phi + ev_0$$
$$v_0 = \dfrac{hv}{e} - \dfrac{\phi}{e}$$
$$v_0$$ is zero fro $$v = 4\times 10^{14}Hz$$
$$0 = \dfrac{hv}{e} - \dfrac{\phi}{e} \Rightarrow \phi = hv$$
$$= \dfrac{6.63 \times 10^{-34} \times 4 \times 10^{14}}{1.6 \times 10^{-19}} = 1.66 eV$$.