Number of elements from the following that $CANNOT$ form compounds with valencies which match with their respective group valencies is
$B, C, N, S, O, F, P, Al, Si$

Which among the following pairs of elements show the highest oxidation state of $+7$ in their different compounds? (Atomic numbers: $Cr=24, V=23, Mn=25, Cl=17, S=16$)

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?

The formula of the oxide of an element $M$ having $IE_1 = 100 \ kJ/mol$,$IE_2 = 250 \ kJ/mol$ and $IE_3 = 1500 \ kJ/mol$ should be:

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

The lowest oxidation number of an atom $B$ in a compound $A_2 B$ is $-2$. The number of electrons in its valence shell is: