Give one example each of:
$(a)$ Triatomic element
$(b)$ Monoatomic molecule
$(c)$ Polyatomic element
$(d)$ Polyatomic ion

(N/A) $O_3$ (Ozone) is a triatomic element because it consists of three oxygen atoms.
$(b)$ $Ar$ (Argon) is a monoatomic molecule as it is a noble gas and exists as a single atom.
$(c)$ $S_8$ (Sulphur) is a polyatomic element because its molecule consists of eight sulphur atoms.
$(d)$ $SO_4^{2-}$ (Sulphate) or $NH_4^+$ (Ammonium) are examples of polyatomic ions,which are ions consisting of more than one atom.