Question:
For the following Assertion and Reason, the correct option is
Assertion (A): When $\mathrm{Cu}$ (II) and sulphide ions are mixed, they react together extremely quickly to give a solid.
Reason (R): The equilibrium constant of $\mathrm{Cu}^{2+}(\mathrm{aq})+$ $\mathrm{S}^{2-}(\mathrm{aq}) \rightleftharpoons \mathrm{CuS}(\mathrm{s})$ is high because the solubility product is low.
Correct Option: , 4
Solution:
Cesium has lowest ionisation enthalpy and hence it shows photoelectric effect to the maximum extent. So, it is used in photo electric cell.