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 18 electrons in each. As they have same atomic number but different masses, so they are also isotopes