Which of the following compounds contains S atom in its ring?

Which element from following combines with hydrogen to form a compound with lowest thermal stability?

What is the decreasing order of deposition of metal on electrode if standard reduction potentials are given as -

$\mathrm{Ag}^{+}\left|\mathrm{Ag}=0.80 \mathrm{~V}, \mathrm{Cu}^{2+}\right| \mathrm{Cu}=0.337 \mathrm{~V}$

$\mathrm{Sn}^{2+}\left|\mathrm{Sn}=-0.136 \mathrm{~V}, \mathrm{Cd}^{2+}\right| \mathrm{Cd}=-0.403 \mathrm{~V}$

If $x=\sin \theta, y=\sin ^3 \theta$, then $\frac{\mathrm{d}^2 y}{\mathrm{~d} x^2}$ at $\theta=\frac{\pi}{2}$ is