Question

Which of the following order is wrong?

(a) NH₃ < PH₃ < AsH₃ - acidic

(b) Li < Be < B < C - 1^st IP

(c) Al₂O₃ < MgO < Na₂O < K₂O - basic

(d) Li⁺ < Na⁺ < K⁺ < Cs⁺ ionic radius.

Answer 1

Correct option (b) Li < Be < B < C - 1^st IP

Explanation :

Li, Be, B, C - these elements belong to the same period. Generally the value of 1^st ionisation potential increases in moving from left to right in a period, since the nuclear charge of the elements also increase in the same direction. But the ionisation potential of boron (B → 2s² p¹) is lower than that of beryllium (Be → 2s²), since in case of boron, 2p¹ electron have to be removed to get B⁺ [B (2s² p¹) → B⁺ (2s²) + e^-], while in case of Be, 2s² electron have to be removed to get Be⁺ (2s¹). p electron can be removed more easily than s electron so the energy required to remove electron will be less in case of boron. The order will be 

Li < B < Be < C.