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Q.
Which of the following element(s) is used as electrode(s) in photoelectric cells?
The s-Block Elements
Solution:
When $Cs$ and $K$ are irradiated with light, the light energy absorbed may be sufficient to make the metal atom to lose an electron. This property makes $Cs$ and $K$ useful as electrodes in photoelectric cell.
Sodium cannot be used due to its smaller size as compared to $K$ and $Cr$.