CBSE Class 12 · 2005 · Foreign · d and f Block ElementsShort Answer

Identify the first-row transition metal ions which have outer electronic configurations of 3d⁴ and 3d⁶, and describe their oxidation states.

Answer: 3d⁴: Cr²⁺ (+2) and Mn³⁺ (+3). 3d⁶: Fe²⁺ (+2) and Co³⁺ (+3).

Solution

^{4}

ions: Cr

^{2 +}

(Cr, Z = 24, in the +2 state) and Mn

^{3 +}

(Mn, Z = 25, in the +3 state). Cr

^{2 +}

tends to oxidise to d

^{3}

^{3 +}

(reducing), Mn

^{3 +}

tends to reduce to d

^{5}

^{2 +}

(oxidising).
3d

^{6}

ions: Fe

^{2 +}

(Fe, Z = 26, +2) and Co

^{3 +}

(Co, Z = 27, +3). Fe

^{2 +}

is oxidisable to the more stable Fe

^{3 +}

^{5}

); Co

^{3 +}

is a strong oxidant in simple salts though stabilised by strong-field ligands.

CBSE Class 12 Board · 2005 · Foreign · Subjective