Here it is
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Magnetic moment=[n(n+2)]^1/2=1.73
n is the number of unpaired electrons

Its value is given so we can calculate n value ( you get a quadratic equation n² +2n -2.9929=0)
n = 1
It means vanadium has only one unpaired electron
In VCl₂ V is with +2 Oxdation Number
V ²⁺  electronic configurations is 
1s²2s²2p⁶3s²3p⁶ 3d³
All three d electrons are unpaired due to Hund's rule

In VCl₃ V is with +3 Oxdation Number
V ³⁺  electronic configurations is 
1s²2s²2p⁶3s²3p⁶ 3d²
All two d electrons are unpaired due to Hund's rule

In VCl₄ V is with +4 Oxdation Number
V ⁴⁺  electronic configurations is 
1s²2s²2p⁶3s²3p⁶ 3d¹
one d electrons is unpaired and this should be the answer.

In VCl₅ V is with +5 Oxdation Number
V ⁵⁺  electronic configurations is 
1s²2s²2p⁶3s²3p⁶
No unpaired electron and it should be diamagentic.