Carbon has a valency of $2$ in $CO$ and $4$ in $CO_2$ and $CH_4$. Its valency in acetylene $(C_2H_2)$ is

Consider the following information about elements $P$ and $Q$:

Element	Period and Group
$Q$	Period $2$,Group $15$
$P$	Period $3$,Group $2$

Then the formula of the compound formed by $P$ and $Q$ elements is:

Which of the following elements exhibits a valency of $2$?

An element $(A)$ occurs in the short period having electronic configuration $ns^2 np^1$. The formula of its oxide will be

Select the $CORRECT$ order of stability.

In view of the signs of $\Delta_{r} G^{\circ}$ for the following reactions:
$PbO_2 + Pb \longrightarrow 2 PbO, \Delta_{r} G^{\circ} < 0$
$SnO_2 + Sn \longrightarrow 2 SnO, \Delta_{r} G^{\circ} > 0$
Which oxidation states are more characteristic for lead and tin?