Use photoelectric effect facts

For photoelectric emission:

• A metal emits electrons only if the incident light frequency is greater than the threshold frequency $\nu_0$.
• The maximum kinetic energy is given by Einstein’s photoelectric equation: $K_{\max} = h\nu - \phi$ where $h$ is Planck’s constant, $\nu$ is the frequency of incident light, and $\phi$ is the work function.

Check Statement I

Statement I says: among microwaves, infrared rays, and ultraviolet rays, ultraviolet rays are most effective for emission of electrons from a metallic surface.

Frequency order is: $\nu_{\text{microwave}} < \nu_{\text{infrared}} < \nu_{\text{ultraviolet}}$

Since photoelectric emission depends on sufficiently high frequency, ultraviolet radiation is the most effective among these.

So, Statement I is true.

Check Statement II

Statement II says: above threshold frequency, the maximum kinetic energy of photoelectrons is inversely proportional to the frequency of incident light.

But from $K_{\max} = h\nu - \phi$ we see that $K_{\max}$ increases linearly with frequency $\nu$.

Therefore, it is not inversely proportional to frequency.

So, Statement II is false.

Choose the correct option

• Statement I: True
• Statement II: False

Hence, the correct option is: $\boxed{\text{B}}$