Question

Which of the following element(s) is used as electrode(s) in photoelectric cells?

• A. Sodium
• B. Caesium
• C. Potassium
• D. Both (b) and (c)

Answer 1

Answer: (D)

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 $Cr$.