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:

Assertion : $HClO_4$ is a stronger acid than $HClO_3$.
Reason : Oxidation state of $Cl$ in $HClO_4$ is $+VII$ and in $HClO_3$ is $+V$.

Which of the following elements exhibits both positive and negative oxidation states?

Which is true for an element $R$ present in $III$ group of the periodic table?

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

Predict the formulas of the stable binary compounds that would be formed by the combination of the following pairs of elements.
$(a)$ Lithium and oxygen
$(b)$ Magnesium and nitrogen
$(c)$ Aluminium and iodine
$(d)$ Silicon and oxygen
$(e)$ Phosphorus and fluorine
$(f)$ Element $71$ and fluorine