Q54 / 180 · AIIMS 2002 · Chemistry

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

  • Correct answer
    A
    If both the assertion and reason are true and reason is a correct explanation of the assertion.
  • B
    If both assertion and reason are true but assertion 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.

Solution

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. $\mathrm{K}$ and $\mathrm{Cs}$ are used in photoelectric cells which are sensitive to blue light.

Hence, the correct answer is option: 'A'.

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