The characteristic shown by the catalyst is known as catalytic selectivity, i.e, the catalyst determines the products formed. For example,

1. If CO and H₂ react in the presence of Ni (nickel) as catalyst the product is methane.
2. If CO and H₂ react in the presence of Cu (copper) as catalyst the product formed is methanol.

Coordination number and oxidation state of the given compound is given as,

Coordination no. = denticity × number of ligand

Coordination number = 2 × 2 + 2 × 1 = 6

Charge on ligand + O.S. of metal ion = charge on complex

– 2 + x = 0

⇒ x = +2

The non-stoichiometry reflect the ease of oxidation of Fe²⁺ to Fe³⁺ effectively replacing a small portion of Fe²⁺ with two thirds their number of Fe³⁺. Thus for every three 'missing' Fe²⁺ ions, the crystal contains two Fe³⁺ ions to balance the charge.   i.e. 3Fe²⁺ = 2Fe³⁺ to maintain electrical neutrality.

Balanced chemical equations:

$5F{e}^{+2} + 2Mn{O}_4^{-} + 8H^{+} \stackrel{ }{\to } 5F{e}^{+3} + 2M{n}^{+2} + 4H_{2}O$

Balanced chemical equation:
$2Mn{O}_4^{-} + H_{2}O + I^{-} \stackrel{ }{\to } 2Mn{O}_2 + 2O{H}^{-} + I{O}_3^{-}$