The correct statements among the following are :

A. Basic vanadium oxide is used in the manufacture of $\mathrm{H}_2 \mathrm{SO}_4$.

B. The spin-only magnetic moment value of the transition metal halide employed in Ziegler-Natta polymerization is 2.84 BM .

C. The p-block metal compound employed in Ziegler-Natta polymerization has the metal in +3 oxidation state.

D. The number of electrons present in the outer most ' d ' orbital of metal halide employed in Wacker process is 8.

Choose the correct answer from the options given below :

A paper dipped in a dil. $\mathrm{H}_2 \mathrm{SO}_4$ solution of ' $X$ ' upon treatment with $\mathrm{SO}_2$ gas turns into green. The compound ' $X$ ' is :

Which of the following is NOT a physical or chemical characteristics of interstitial compounds?

Pairs of elements with the same number of electrons in their respective 4f orbital are

[Atomic number. Eu-63, Gd-64, Dy-66, Ho-67, Tm-69, Yb-70, Lu-71, Hf-72]

A. (Eu and Gd)

B. (Dy and Ho)

C. ( Yb and Hf )

D. ( Lu and Tm)

Choose the correct answer from the options given below :