(i) Threshold frequency of P is $$3\times10^{14}Hz.$$
Threshold frequency of Q is $$6\times10^{14}Hz.$$
Clearly Q has higher threshold frequency.
(ii) Work function of metal Q,$$\psi_0=hv_0$$
$$=(6.6\times10^{-34})\times6\times10^{14}J$$
$$=\dfrac{39.6\times10^{-20}}{1.6\times10^{-19}}eV=2.5eV$$
(iii) Maximum kinetic energy, $$K_{max}=hv-hv_0$$
$$=h(v-v_0)$$
$$=6.6\times10^{-34}(8\times10^{14}-6\times10^{14})$$
$$=6.6\times10^{-34}\times2\times10^{14}J$$
$$=\dfrac{6.6\times10^{-34}\times2\times10^{14}J}{1.6\times10^{-19}}eV$$
$$\therefore K_{max}=0.83eV$$