In which one of the following pairs, the two species are both isoelectronic and isotopic ? (At. Numbers : Ca = 20, Ar = 18, K = 19, Mg = 12, Fe = 26, Na = 11)

Options

A. `.^(40)Ca^(2-)` and `.^(40)Ar`
B. `.^(39)K^(+)` and `.^(40)K^(+)`
C. `.^(24)Mg^(2+)` and `.^(25)Mg`
D. `.^(23)Na` and `.^(24)Na^(+)`

Answer

B

Explanation

In (B), `K^(+)` has 1g electrons in each. As they have same at atomic number but different masses, they are isotopes also.