4AB › Chemistry PYQ › CSIR-NET › December 2019 › Q57Q57 · CSIR-NET Chemistry, December 2019 Paper: CSIR-NET December 2019 · Subject: Inorganic Chemistry · Chapter: Acids and Bases · Topic: Acids & Bases – General · Marks: 2 · Difficulty: Easy
Choose the equilibria from the following that are NOT favoured to go to right \[ \begin{array}{l} \text{(A) } \mathrm{As_2S_5}+5\mathrm{HgO} \xrightarrow{\text{gives}} \mathrm{As_2O_5}+5\mathrm{HgS} \\ \text{(B) } \mathrm{La_2(CO_3)_3}+\mathrm{Bi_2S_3} \xrightarrow{\text{gives}} \mathrm{La_2S_3}+\mathrm{Bi_2(CO_3)_3} \\ \text{(C) } \mathrm{CaSO_4}+\mathrm{CaS} \xrightarrow{\text{gives}} \mathrm{CdS}+\mathrm{CaSO_4} \\ \text{(D) } \mathrm{BeF_2}+\mathrm{HgI_2} \xrightarrow{\text{gives}} \mathrm{BeI_2}+\mathrm{HgF_2} \end{array} \]
(a) A and B
(b) A and C
(c) B and C
(d) B and D
Answer Answer: D ✓ checked by 4AB · confidence high
The source book printed B; on checking, D is correct — see the explanation.
Explanation HSAB: the hard cation La³⁺ prefers carbonate (O) over sulfide, and Be²⁺ prefers F⁻ while soft Hg²⁺ prefers I⁻. So B and D are not favoured to the right. A and C go right, forming the soft–soft HgS and CdS (d).
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