Question

which is greater in size fe2+ or fe3+

Answer 1

fe3+ is greater in size due to greater per elecron nuclear charge

Answer 2

$Fe^{2+} \ \textgreater \ Fe^{3+}$

Reason:

Fe2+ means loss of 2 electron
and
Fe3+ means loss  of 3 electron which gives poor shielding effect and strong nuclear attraction  hence the size gets decrease of Fe3+