Question

Which of the following order is wrong:

• A. $N{H}_3<P{H}_3<As{H}_3$ - Acidic
• B. $Li<Be<B<C$ - First IP
• C. $A{l}_2{O}_3<MgO<N{a}_{2}O<K_{2}O$ - Basic
• D. $L{i}^{+}<N{a}^{+}<K^{+}<C{s}^{+}$ - lonic radius

Answer 1

Answer: (B)

The acidic character of hydrides of group 15 increases from $N{H}_{3}toBi{H}_3$ . This trend is largely due to changes in the electronegativity and size of the nonmetal atom. Across a period from left to right, the ionisation energy increases. This is due to the increase in nuclear charge having a greater pull on the electrons and therefore more energy is required to remove electrons. As more energy is required to take the electron from s-orbital than the p-orbital, beryllium has more ionisation energy than boron. $Li<Be>B<C$ is the correct order in the first four elements of the second period. The more electronegative the central atom, the more acidic the oxide. Electropositive character increases from right to left across the periodic table and increases down the column. $A{l}_2{O}_3<MgO<N{a}_{2}O<K_{2}O$ is the correct order of basic nature. Down the group ionic size increases. Hence, $L{i}^{+}<N{a}^{+}<K^{+}<C{s}^{+}$ is the correct order.