Which of the following arrangements does not represent the correct ord...
A) V^2+<Cr^2+<Mn^2+<Fe^2+ : paramagnetic behaviour
Electronic configuration of V^2+ = 3d^3 ; n=3
Electronic configuration of Cr^2+=3d^4 ; n=4
Electronic configuration of Mn^2+=3d^5 ; n=5
Electronic configuration of Fe^2+=3d^6 ; n=4
Here, Mn2+ has maximum number of unpaired electrons and so its most paramagentic. Therefore the correct order is :
V^2+<Cr^2+<Mn^2+
B) Ni^2+<Co^2+<Fe^2+<Mn^2+ : Ionic size
We know for the same oxidation state, the ionic radii generally decrease with increase in nuclear charge and the nuclear charge increase as we move across a period. Therefore, the given order is correct.
C) Co^3+<Fe^3+<Cr^3+<Sc^3+ : Stability in aqueous solution
The lower the electrode potential, i.e. more negative the standard reduction potential of the electrode, the more stable is the transition metal in aqueous solution. The value becomes less negative across the series. Therefore, the given order is correct.
D)Sc<Ti<Cr<Mn : number of oxidation states
The given order is correct as Mn shows maximum number of oxidation states i.e. upto +7 (due to its configuration 3d^5 4s^2 it can have maximum oxidation states). Sc on the other hand shows least oxidation state.
Therefore, (B) doesnot show correct order of property.