Magnetic moment 2.84 B.M. is given by :
(At. nos. Ni = 28, Ti = 22, Cr = 24, Co = 27)

Ni²⁺ = 3d⁸ = 

number of unpaired electrons (r) in Ni²⁺ = 2
$\because \mathrm{\mu }=\sqrt{\mathrm{n}(\mathrm{n}+2)}=\sqrt{2(2+2)}=\sqrt{8}=2.8\mathrm{BM}$
Hence $\mathrm{\mu }$ = 2.8 B.M., thus Ni²⁺ is paramagnetic