CBSE Class 12 · 2008 · Foreign · d and f Block ElementsShort Answer

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Compare the relative stability of the +2 oxidation state in aqueous solution for the metals having the outer electronic configurations 3d³4s², 3d⁶4s² and 3d⁵4s².

Answer: Stability of M²⁺: 3d⁵4s² (Mn²⁺, d⁵ half-filled) > 3d⁶4s² (Fe²⁺, d⁶) > 3d³4s² (V²⁺, d³ — readily oxidised to V³⁺).

Solution

Each M

^{2 +}

forms by losing the two 4s electrons:
3d

^{5}

^{2}

(Mn) → Mn

^{2 +}

= 3d

^{5}

: exactly half-filled, maximum exchange energy — most stable +2 ion.
3d

^{6}

^{2}

(Fe) → Fe

^{2 +}

= 3d

^{6}

: moderately stable, but oxidisable to d

^{5}

^{3 +}

.
3d

^{3}

^{2}

(V) → V

^{2 +}

= 3d

^{3}

: least stable of the three in water; it is readily oxidised to V

^{3 +}

/VO

^{2 +}

M n^{2 +} (d^{5}) > F e^{2 +} (d^{6}) > V^{2 +} (d^{3})

CBSE Class 12 Board · 2008 · Foreign · Subjective

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CBSE Class 12 · 2008 · Foreign · d and f Block ElementsShort Answer

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