The nucleus of an element contains $9$ protons. Its valency would be:

What will be the formula of the compound formed between the following elements?
$(i)$ The element with atomic number $19$ and iodine.
$(ii)$ The first element and oxygen.

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

The valency (oxidation state) of phosphorus in $H_3PO_4$ is

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:

Consider the elements:
$Cs, Ne, I$ and $F$
$(a)$ Identify the element that exhibits only negative oxidation state.
$(b)$ Identify the element that exhibits only positive oxidation state.
$(c)$ Identify the element that exhibits both positive and negative oxidation states.
$(d)$ Identify the element which exhibits neither the negative nor does the positive oxidation state.