Statement-1: Potassium and caesium are used in photo-electric cells.
Statement-2: Potassium and caesium emit electrons on exposure to light above certain minimum frequency.

Options

A. If both the assertion and reason are true and reason is correct explanation of the assertion .
B. If both the assertion and reason are true but reason is not a correct explanation of the assertion .
C. If the assertion is true but the reason is false.
D. If both assertion and reason are false.

Answer

A

Explanation

The valence shell electron in the alkali metals is so loosely held that even the low energy photons ( light) can eject this electron from the metal surface. This phenomenon is called as photoelectric effect , K and Cs are used in photoelectric cells which are sensitive to blue light.