Q32 · CSIR-NET Chemistry, December 2011
Paper: CSIR-NET December 2011 · Subject: Inorganic Chemistry · Chapter: Acids and Bases · Topic: Acids & Bases – General · Marks: 2 · Difficulty: Hard
The correct order of acidity among the following species is
(a)$\left[\mathrm{Na}\left(\mathrm{H}_{2} \mathrm{O}\right)_{6}\right]^{+}>\left[\mathrm{Ni}\left(\mathrm{H}_{2} \mathrm{O}\right)_{6}\right]^{2+}>\left[\mathrm{Mn}\left(\mathrm{H}_{2} \mathrm{O}\right)_{6}\right]^{2+}>\left[\mathrm{Sc}\left(\mathrm{H}_{2} \mathrm{O}\right)_{6}\right]^{3+}$
(b)$\left[\mathrm{Sc}\left(\mathrm{H}_{2} \mathrm{O}\right)_{6}\right]^{3+}>\left[\mathrm{Ni}\left(\mathrm{H}_{2} \mathrm{O}\right)_{6}\right]^{2+}>\left[\mathrm{Mn}\left(\mathrm{H}_{2} \mathrm{O}\right)_{6}\right]^{2+}>\left[\mathrm{Na}\left(\mathrm{H}_{2} \mathrm{O}\right)_{6}\right]^{+}$
(c)$\left[\mathrm{Mn}\left(\mathrm{H}_{2} \mathrm{O}\right)_{6}\right]^{2+}>\left[\mathrm{Ni}\left(\mathrm{H}_{2} \mathrm{O}\right)_{6}\right]^{2+}>\left[\mathrm{Sc}\left(\mathrm{H}_{2} \mathrm{O}\right)_{6}\right]^{3+}>\left[\mathrm{Na}\left(\mathrm{H}_{2} \mathrm{O}\right)_{6}\right]^{+}$
(d)$\left[\mathrm{Sc}\left(\mathrm{H}_{2} \mathrm{O}\right)_{6}\right]^{3+}>\left[\mathrm{Na}\left(\mathrm{H}_{2} \mathrm{O}\right)_{6}\right]^{+}>\left[\mathrm{Ni}\left(\mathrm{H}_{2} \mathrm{O}\right)_{6}\right]^{2+}>\left[\mathrm{Mn}\left(\mathrm{H}_{2} \mathrm{O}\right)_{6}\right]^{2+}$
Answer
Answer: B ✓ checked by 4AB · confidence high
Explanation
Acidity of aqua ions rises with charge and charge density: Sc³⁺ > Ni²⁺ (smaller) > Mn²⁺ > Na⁺.
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