Which of the following orders is incorrect with respect to the property indicated ?

Which of the following orders is incorrect with respect to the property indicated ?
  1. NH3<PH3<AsH3  (acidic behaviour)
  2. Li<Be<B<C  (first ionisation energy)
  3. Al2O3<MgO<Na2O<K2O  (basic character)
  4. Li+<Na+<K+<Cs+  (ionic radius)

Solution

(i) Bond angle of NH 3 = 107 o
PH 3  >  AsH 3 = 90 o
According to bond angle the %s character of lp in NH 3 =22% while in PH 3  &  AsH 3 having approximately 100%, so the donation of lp in PH 3  &  AsH 3 are difficult. Hence, the acidic character increases and the order of acidic character is NH 3 < PH 3 < AsH 3 is correct
(ii) On moving left to right in a period ionisation energy increases. Li<Be<B<C but the first ionisation potential of Be is higher than that of B because Be has fulfilled configuration.
(iii) Metallic character increases hence the basic character of oxide increases.
(iv) In a group from top to the bottom, the number of the shell increases hence radius increases.

Asked in: MHT CET Full Test 13

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