Which of the following are paramagnetic?

Question

A) V^3+
B)Cd^2+
C)Co^3+
D)Ag^+

I dont understand which ones are paramagnetic?

why would V^3+ be [Ar] 3d^2 wouldnt it be [Ar]4s^2 because V^3+ would have 20 electrons so you go to Ar with has 18 electrons and you need 2 more and then next orbital is 4s not 3d because Ar ends at 3p right?

Answer 1

Look at the proton number, and work out how many d electrons in total there must be in each metal atom. Then take one electron off for every + charge. Then work out if any of them are unpaired. If so, the ion is paramagnetic.

For example, V = 23, V 3+ has 20 electrons which is therefore called [Ar]3d2. Now these two d electrons occupy separate orbitals, so they are unpaired.