Question

Which of the following is isoelectronic to the noble gas argon?

A. Mg atom, 1s^2 2s^2 2p^6 3s^2

B. Ca atom, 1s^2 2s^2 2p^6 3s^2 3p^4 4s^2

C. Ca2+ ion, 1s^2 2s^2 2p^6 3s^2 3p^6

D. Cl atom, 1s^2 2s^2 2p^6 3s^2 3p^5

E. N3- ion, 1s^2 2s^2 2p^6 3s^2 3p^6

Answer 1

Can anybody explain?

Answer 2

C.

It's difficult to explain if you don't have a good feel about how the electronic configurations are like. Go through them once more. Write out the electronic configurations from Hydrogen and you should see what C is the answer.

I can tell from one look that the other configurations are not noble gases becuase their outer shell is not fully filled/wrong chemical symbol.

Answer 3

N 3- is actually Neon.

Answer 4

Thanks!!!