Two elements $X$ and $Y$ have the following electronic configurations: $X = 1s^2, 2s^2 2p^6, 3s^2 3p^6, 4s^2$ and $Y = 1s^2, 2s^2 2p^6, 3s^2 3p^5$. The expected compound formed by the combination of $X$ and $Y$ is:

Arrange the acids $(I)$ $H_2SO_3$,$(II)$ $H_3PO_3$,and $(III)$ $HClO_3$ in the decreasing order of acidity.

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:

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 $+V$.

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

The number of valence electrons present in an element with atomic number $117$ is