The coordination of $$\mathrm{Ni^2+}$$ is 4.

$$\mathrm{NiCl_2+KCN}$$ (excess) $$\to$$ A (cyano complex)

$$\mathrm{NiCl_2+ conc.~HCl}$$ (excess) $$\to$$ B (chloro complex)

The IUPAC names of $$\mathbf{A}$$ and $$\mathbf{B}$$ are

The edge length of unit cell of a metal having molecular weight $$75 \mathrm{~g} \mathrm{~mol}^{-1}$$ is 5 $$\mathop A\limits^o $$ which crystallizes in cubic lattice. If the density is $$2 \mathrm{~g} / \mathrm{cc}$$, find the radius of metal atom. $$\left(\mathrm{N}_{\mathrm{A}}=6 \times 10^{23}\right)$$. Give the answer in $$\mathrm{pm}$$.

$$ \mathrm{B}(\mathrm{OH})_3+\mathrm{NaOH} \quad \mathrm{NaBO}_2+\mathrm{Na}\left[\mathrm{~B}(\mathrm{OH})_4\right] $$$+\mathrm{H}_2 \mathrm{O}$

How can this reaction be made to proceed in forward direction?

A solution when diluted with $\mathrm{H}_2 \mathrm{O}$ and boiled, it gives a white precipitate. On addition of excess $\mathrm{NH}_4 \mathrm{Cl} / \mathrm{NH}_4 \mathrm{OH}$, the volume of precipitate decreases leaving behind a white gelatinous precipitate. Identify the precipitate which dissolves in $\mathrm{NH}_4 \mathrm{OH} / \mathrm{NH}_4 \mathrm{Cl}$.