Which of the following arrangements does not represent the correct order of the property stated against it ?
(i) `Ni^(2+) lt Co^(2+) lt Fe^(2+) lt Mn^(2+)` : ionic size
(ii) `Co^(3+) lt Fe^(3+) lt Cr^(3+) lt Sc^(3+)` : stability in aqueious solution
(iii) `Sc lt Ti lt Cr lt Mn` : number of oxidation states
(iv) `V^(2+) lt Cr^(2+) lt Mn^(2+) lt Fe^(2+)` : paramagnetic behaviour

Options

A. (i), (ii), (iii), (iv)
B. (i), (ii), (iii)
C. (ii) and (iv)
D. (ii) and (iii)

Answer

B

Explanation

As we move across the period the ionic size decreases:
`{:(Mn^(2+),gt,Fe^(2+),gt,Co^(2+),gt,Ni^(2+)),((82"pm"),,(77"pm"),,(74"pm"),,(70"pm")):}`
Stability in aqueous solution is related to the extent of hydration. Smaller the ion, (for a given charge), higher the charge density and hence greater the extent of hydration. As we move across the period `(Sc^(3+) rarr Cr^(3+) rarr Fe^(3+) rarr Co^(3+))`, the ionic size usually decreases. `Sc^(3+)` with the largest size is least hydrated and hence least stable. As we move across the seris `(Sc rarr Tio rarr Cr rarr Mn)`, the number of unpaired d electrons increases and hence number of oxidation states.
`V^(2+) (Z = 23) implies 3d^(3) implies 3` unpaired electrons.
`Cr^(2+) (Z = 24) implies 3d^(4) implies 4` unpaired electrons.
`Mn^(2+) (Z = 25) implies 3d^(5) implies 5` unpaired electrons.
`Fe^(2+) (Z = 26) implies 3d^(6) implies 4` unpaired electrons.
`Fe^(2+)` is less paramgentic than `Mn^(2+)`