Question

Which of the following arrangements does not represent the correct order of the property stated against it ?

(a) V2+ < Cr2+ < Mn2+ < Fe2+ : paramagnetic behaviour

(b) Ni2+ < Co2+ < Fe2+ < Mn2+ : ionic size

(c) Co3+ < Fe3+ < Cr3+ < Sc3+ : stability in aqueous solution

(d) Sc < Ti < Cr < Mn : number of oxidation states

Answer 1

Correct option: (a) V2+ < Cr2+< Mn2+< Fe2+ : paramagnetic behaviour

Explanation:

V = 3d3 4s 2 ; V2+ = 3d 3 = 3 unpaired electrons

Cr = 3d5 4s1 ; Cr2+ = 3d 4 = 4 unpaired electrons

Mn = 3d5 4s2 ; Mn2+ = 3d 5 = 5 unpaired electrons

Fe = 3d6 4s 2 ; Fe2+ = 3d 6 = 4 unpaired electrons

Hence the correct order of paramagnetic behaviour V2+ < Cr2+ = Fe2+ < Mn2+

b) For the same oxidation state, the ionic radii generally decreases as the atomic number increases in a particular transition series. Hence the order is Mn2+ > Fe2+ > Co2+ > Ni2+

(c) In solution, the stability of the compound depends upon electrode potentials, SEP of the transitions metal ions are given as Co3+ / Co = + 1.97, Fe3+ / Fe = + 0.77 ; Cr3+ / Cr2+ = – 0.41, Sc 3+ is highly stable as it does not show + 2 O. *.