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

In which one of the following pairs, the two species are both isoelect

1.	In which one of the following pairs, the two species are both isoelectronic and isotopic ? (Atomic number : Ca = 20, Ar = 18, K = 19, Mg = 12, Fe = 26, Na= 11)
Answer» `.^(40)Ca^(2+) and .^(40)Ar` `._(39)K^(+) and .^(40)K^(+)` `.^(24)Mg^(2+) and .^(25)Mg` `.^(23)Na and .^(24)Na^(+)` Solution :In (b), `K^(+)` has 18 ELECTRONS in each. As they have same atomic number but DIFFERENT masses, so they are ALSO isotopes