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.

(N/A) The electronic configuration is determined by the atomic number $(Z)$:
Sulphur $(S)$: Atomic number $Z = 16$. Electronic configuration: $2, 8, 6$.
Oxygen $(O)$: Atomic number $Z = 8$. Electronic configuration: $2, 6$.
$(b)$ Valency is the combining capacity of an element.
For Oxygen $(O)$: It needs $2$ electrons to complete its octet,so its valency is $2$.
For Sulphur $(S)$: It needs $2$ electrons to complete its octet,so its valency is $2$.
$(c)$ No,they are not isotopes. Isotopes are atoms of the same element having the same atomic number but different mass numbers. Since sulphur and oxygen have different atomic numbers ($16$ and $8$ respectively),they are different elements.