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)

Which two species of the following pairs are not isoelectronic -

Which one of the following sets of ions represents the collection of isoelectronic species? (Atomic numbers : F = 9, CI = 17, Na = 11, Mg = 12,Al = 13, K = 19, Ca = 20, Sc =21)

Which of the following pairs are isoelectronic ? Na, Mg

In which of the following pair, both the species are isoelectronic but the first one is large in size than the second?

In which of the following pair, both the species are isoelectronic but the first one is large in size than the second?