Calculate number of proton , neutron and electron in element potassium with atomic number 19 and mass number 39.

Explanation

In aqueous solution of sodium chloride, the salt sodium chloride and water ionises as follows :
`NaCloverset(aq.)rarrNa^(+)(aq)+Cl^(-)(aq),H_(2)OiffH^(+)(aq)+OH^(-)(aq)`
At cathode : Both `Na^(+) and H^(+)` ions migrate towards the cathode. However, `H^(+)` ions are discharged in preference to `Na^(+)`. This is due to lesser dicharge potential of `H^(+)` ions. `Na^(+)` ions remain in solution.
`H^(+)(aq)+e^(-)rarrH(g),H(g)+H(g)rarrH_(2)(g)`
At anode: Both `Cl^(-) and OH^(-)` ions migrate towards the anode. However, `Cl^(-)` ions are discharged in preference to `OH^(-)` ions. `OH^(-)` ions remain in solution.
`Cl^(-)(aq)rarrCl(g)+e^(-),Cl(g)+Cl(g)rarrCl_(2)(g)`
Thus, during the electrolysis of aqueous sodium chloride, `H_(2)` gas is evolved at cathode while `Cl_(2)` gas at anode.