The nucleus of an element contains $9$ protons. Its valency would 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 $+V$.

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:

The oxidation state of $+1$ for phosphorus is found in:

The group number,number of valence electrons,and valency of an element with atomic number $15$,respectively,are