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

If the electronic configuration of $M = 2, 8, 3$ and that of $A = 2, 8, 7$,the formula of the compound is

The atomic number of an element which shows the oxidation state of $+3$ is

Which of the oxidation state$(s)$ is/are shown by the element sulphur?

What is the oxidation state of chlorine in its weakest oxoacid?

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?