Highest oxidation state of Mn is exhibited in $$\mathrm{Mn_2O_7}$$. The correct statements about $$\mathrm{Mn_2O_7}$$ are

(A) Mn is tetrahedrally surrounded by oxygen atoms.

(B) Mn is octahedrally surrounded by oxygen atoms.

(C) Contains Mn-O-Mn bridge.

(D) Contains Mn-Mn bond.

Choose the correct answer from the options given below :

When $$\mathrm{Cu}^{2+}$$ ion is treated with $$\mathrm{KI}$$, a white precipitate, $$\mathrm{X}$$ appears in solution. The solution is titrated with sodium thiosulphate, the compound $$\mathrm{Y}$$ is formed. $$\mathrm{X}$$ and $$\mathrm{Y}$$ respectively are :

$$\mathrm{Nd^{2+}}$$ = __________

The correct order of basicity of oxides of vanadium is :