The electrode reaction is:
Ni2+1 mole+2e−2×96500 C→Ni
Quantity of electric charge passed
=3.7×6×60×60 coulomb=79920 coulomb
Number of moles of Ni(NO3)2 decomposed or nickel deposited
=12×96500×79920=0.4140
Number of moles of Ni(NO3)2 present before electrolysis
=0.5×2=1.0
Number of moles of Ni(NO3)2 present after electrolysis
=(1.0−0.4140)=0.586
Since, 0.586 moles are present in 0.5 litre,
Molarity of the solution =2×0.586=1.72 M
When nickel electrodes are used, anodic nickel will dissolve and get deposited at the cathode. The molarity of the solution will, thus, remain unaffected.