Question

The increasing order of polarising power is:

• A. ${Ca}^{2+}<{Mg}^{2+}<{Be}^{2+}<K^{+}$
• B. ${Mg}^{2+}<{Be}^{2+}<K^{+}<{Ca}^{2+}$
• C. ${Be}^{2+}<K^{+}<{Ca}^{2+}<{Mg}^{2+}$
• D. $K^{+}<{Ca}^{2+}<{Mg}^{2+}<{Be}^{2+}$

Answer 1

The correct option is D $K^{+}<{Ca}^{2+}<{Mg}^{2+}<{Be}^{2+}$

The increasing order of polarising power is $K^{+}<{Ca}^{2+}<{Mg}^{2+}<{Be}^{2+}$. Charge-size ratio increases and thus polarising power increases.

For $B{e}^{2+},M{g}^{2+},C{a}^{2+}$, since charge is same and size is in the order of $C{a}^{2+}>M{g}^{2+}>B{e}^{2+}$ , the order of polarising power is $C{a}^{2+}<M{g}^{2+}<B{e}^{2+}$.

Charge of $K^{+}$ is lowest and size is larger than ${Ca}^{2+}$ so its polarising power is lowest.