Assertion: Both [Cr(H₂O)₆]²⁺ and [Fe(H2O)₆]²⁺ have same magnetic moment.
Reason: Number of unpaired electrons in Cr²⁺ and Fe²⁺ are same.

Assertion and reason both are correct statements and reason is correct explanation for assertion.

In [Cr(H₂O)₆]²⁺ 

x + 6(0) = 2

x = 2

₂₄Cr : [Ar]4s¹3d⁵

Cr²⁺ = [Ar]3d⁴   (4 unpaired electrons)

In [Fe(H2O)₆]²⁺ 

x + 6(0) = 2

x = 2

₂₆Fe : [Ar]4s²3d⁶

Fe²⁺ : [Ar]3d⁶    ( 4 unpaired electrons)

Both contains same number of unpaired electrons, hence their magnetic moment will be same.

Magnetic moment, u = \(\sqrt {n(n+2)}\) where n is the number of unpaired electrons.