Class 12 NEET Chemistry Coordination Compounds

Odd electrons, ions and molecules are paramagnetic.
In Cr(CO)6 molecule 12 electrons are contributed by CO group and it contains no odd electron.
Cr→3d54s1
Fe(CO)5 molecule also does not contain odd electron.
Fe→3d64s2
In[Fe(CN)6]4− ion Fe(+2)→3d64s0
∴ No odd electrons.
In[Cr(NH3)6]3+ ion Cr(+3)→3d34s0
This ion contains odd electron so it is paramagnetic.