The atomic numbers of three elements $A, B$ and $C$ are $9, 10$ and $13$ respectively. Which of them will form a cation?

Sulphur dioxide $(SO_{2})$ is a colourless,pungent-smelling gas and is a major air pollutant.
$(a)$ Write the electronic configuration of its constituent elements,sulphur and oxygen.
(Given: $_{16}^{32}S, _{8}^{16}O)$
$(b)$ Write the valency of sulphur and oxygen.
$(c)$ Are sulphur and oxygen isotopes of the same element? Explain your answer.

Which of the following correctly represents the electronic distribution in the $Mg$ atom?

State whether the following statement is true or false:
An atom of each element has a definite combining capacity,called its valency.

One electron is present in the outermost shell of the atom of an element $X$. What would be the nature and value of charge on the ion formed if this electron is removed from the outermost shell?

$(a)$ Name the three subatomic particles of an atom.
$(b)$ An atom of an element has $5$ electrons in the $L$ shell.
$(i)$ What is the atomic number of the element?
$(ii)$ State its valency.
$(iii)$ Identify the element and write its name.