Chemistry - Complete d-block Question with Solution | TestHub

A. ${\mathrm{CrO}}_4^{2-}$:  the geometry of chromate ions is tetrahedral.

B. $2{\mathrm{Na}}_2{\mathrm{CrO}}_4+2{\mathrm{H}}^{+}\to {\mathrm{Na}}_2{\mathrm{Cr}}_2{\mathrm{O}}_7+2{\mathrm{Na}}^{+}+{\mathrm{H}}_2\mathrm{O}$

Dichromates are usually prepared from chromates and this is obtained by the combination of chromite ore with sodium/potassium carbonate in the presence of air.

C. Green manganate is paramagnetic with $1$ unpaired electron.

D.

Disproportionation reaction of managanate in acidic or neutral medium is one of the preparation method for the permanaganate.
$$\begin{gathered} 3{\mathrm{MnO}}_4^{2-}+4{\mathrm{H}}^{+}\to 2{\mathrm{MnO}}_4^{-}+{\mathrm{MnO}}_2+2{\mathrm{H}}_2\mathrm{O} \\ \mathrm{Dark} \mathrm{purple} \end{gathered}$$
Here, ${\mathrm{Mn}}^{+6}$ is disproportionate to ${\mathrm{Mn}}^{7+}$ and ${\mathrm{Mn}}^{4+}$.

E. With the increasing oxidation number of transition metal, ionic character of the oxides decreases. This is because on increasing oxidation state of a cation it's size decreases and hence its polarising power increases. According to Fajan's rule smaller is the size of cation greater will be its polarising power and hence, greater will be its covalent character. So ionic character reduces.