JEE Chemistry 2023 Question with Solution

Given: Assertion $A$ states that in the photoelectric effect, electrons are emitted immediately when light of frequency greater than the threshold frequency falls on a metal surface.

Find: Whether Assertion $A$ and Reason $R$ are correct, and whether $R$ explains $A$.

In the photoelectric effect, emission occurs only when the incident light has frequency greater than the threshold frequency. Hence, Assertion $A$ is correct.

Reason $R$ says that when a photon of any energy strikes an electron, transfer of energy takes place. This statement is not correct in the context of photoelectric emission, because mere transfer of energy in any amount does not ensure ejection. The incident photon must provide at least the minimum required energy, that is,

$$h\nu \ge \phi$$

where $\phi$ is the work function.

Therefore, Assertion $A$ is correct but Reason $R$ is not correct. The correct option is A.