Molar ionic conductivities of divalent cation and anion are $$57 \mathrm{~S~cm}^2 \mathrm{~mol}^{-1}$$ and $$73 \mathrm{~S~cm}^2 \mathrm{~mol}^{-1}$$ respectively. The molar conductivity of solution of an electrolyte with the above cation and anion will be:

Identify 'A' in the following reaction :

The statement(s) that are correct about the species $$\mathrm{O}^{2-}, \mathrm{F}^{-}, \mathrm{Na}^{+}$$ and $$\mathrm{Mg}^{2+}$$.

(A) All are isoelectronic

(B) All have the same nuclear charge

(C) $$\mathrm{O}^{2-}$$ has the largest ionic radii

(D) $$\mathrm{Mg}^{2+}$$ has the smallest ionic radii

Choose the most appropriate answer from the options given below :

The reaction at cathode in the cells commonly used in clocks involves.