Question

Potassium and caesium are used in photoelectric cells. Potassium and caesium emit electrons on exposure to light.

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

Answer 1

Answer: (A)

If both assertion and reason are true and reason is a correct explanation of the assertion

Answer 2

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.