Paramagnetism is a property due to the presence of unpaired electrons. In case of transition metals, as they contain unpaired contain unpaired electrons in the `(n-1)` d orbitals , most of the transition metal ions and their compounds are paramagnetic . Paramagnetism increases with increases in number of unpaired electrons. Magnetic moment is calculated from 'spin only formula' `Vz`
`mu=sqrt(n(n+2)) B.M n="number of unpaired electrons"`
Similarly the colour of the compounds of transition metals may be attributed to the presence of incomplete `(n-1)` d sub-shell. When an electron from a lower energy of d-orbitals is excited to a higher energy d-orbital, the energy of excitation corresponds to the frequency of light absorbed. This frequency generally lies in the visible region. The colour observed corresponds to complementry colour of the light obserbed. The frequency of the light absorbed is determined by the nature of the ligand.
Identify the correct statement.

Options

A. `Mn^(2+)` has the highest paramagnetism amongst the bivalent cations of the `I^(st)` transition series.
B. The coloured ions or compounds of transition elements are due to d-d transition only.
C. In `3 d` series the paramagnetic chaacter first increase to maximum & then starts decreasing.
D. `Cr^(2+)` is stroger reducing agent than `Fe^(2+)`

Answer

B

Explanation

I. Colour of ions of compounds of transition metals is due to (i) d-d transition (ii) charge transfer (iii) polarisation
II `d^(4) rarr d^(3)` occurs in case of `Cr^(2+)` to `Cr^(3+)`
`d^(6) rarr d^(5)` occurs in case of `Fe^(2+)` to `Fe^(3+)`