Bond dissociation energy of "E-H" bond of the "$\mathrm{H}_{2} \mathrm{E}$ " hydrides of group 16 elements (given below), follows order.

A. $\mathrm{O}$

B. $\mathrm{S}$

C. Se

D. $\mathrm{Te}$

Choose the correct from the options given below:

Boric acid is solid, whereas $\mathrm{BF}_3$ is gas at room temperature because of :

The correct order of $\mathrm{pK}_{\mathrm{a}}$ values for the following compounds is:

$1 \mathrm{~L}, 0.02 \mathrm{M}$ solution of $\left[\mathrm{Co}\left(\mathrm{NH}_{3}\right)_{5} \mathrm{SO}_{4}\right]$ Br is mixed with $1 \mathrm{~L}, 0.02 \mathrm{M}$ solution of $\left[\mathrm{Co}\left(\mathrm{NH}_{3}\right)_{5} \mathrm{Br}\right] \mathrm{SO}_{4}$. The resulting solution is divided into two equal parts $(\mathrm{X})$ and treated with excess of $\mathrm{AgNO}_{3}$ solution and $\mathrm{BaCl}_{2}$ solution respectively as shown below:

$1 \mathrm{~L}$ Solution $(\mathrm{X})+\mathrm{AgNO}_{3}$ solution (excess) $\longrightarrow \mathrm{Y}$

$1 \mathrm{~L}$ Solution $(\mathrm{X})+\mathrm{BaCl}_{2}$ solution (excess) $\longrightarrow \mathrm{Z}$

The number of moles of $\mathrm{Y}$ and $\mathrm{Z}$ respectively are