A species ‘X’ contains 20 protons and 18 electrons. (A) species ‘Y’ contains 18 protons and 18 electrons. What are ‘X’ and ‘Y’ respectively ?

Options

A. Ca and Ar
B. `Ca^(2+)` and `S^(2-)`
C. `Ca^(2+)` and `CI^(-)`
D. `Ca^(2+)` and Ar

Answer

D

Explanation

(i) X has 20 protons `therefore` atomic number = Z = 20 `therefore` The atom is Ca But it has 18 electrons `therefore` X must be `Ca^(2+)`
(ii) Y has 18 protons `therefore` atomic number = 18 = Z `therefore` The atom is Ar But no. of electron in it are 18 Y must be A