Considering H ₂ O as weak field ligand, the number of unpaired electrons in [ Mn ( H ₂ O )₆ ]²⁺ will be (Atomic number of Mn =25 )

Step-by-step solution

Mn in [ Mn ( H ₂ O )₆ ]²⁺ is present as Mn ²⁺ (3 d^5 ) . s p^3 d^2 hybridisation occurs in [ Mn ( H ₂ O )₆ ]²⁺ . Due to the presence of weak field ligand pairing of electron does not take place, hence the number of unpaired electrons is five.