Description of a few atoms is given in the table.

Atom	$P$	$Q$	$R$	$S$
No. of protons	$17$	$11$	$17$	$9$
No. of neutrons	$18$	$12$	$20$	$10$
No. of electrons	$17$	$10$	$17$	$10$

Identify a cation, an anion and a pair of isotopes from the given table:

	Cation	Anion	Pair of isotopes
(A)	$P$	$Q$	$P,Q$
(B)	$Q$	$S$	$P,R$
(C)	$R$	$P$	$R,S$
(D)	$Q$	$S$	$Q,S$