Correct Answer - B
`Ni^(2+)+"excess"NH_3(aq)tounderset("deep blue coloured solution")([Ni(NH_3)_6]^(2+))`
`Ni^(2+), 3d^8, t_(2g)^(2,2,2)e_g^(1,1)implies sp^3d^2`
n=2 paramagnetic & octahedral complex `Co^(3+), 3d^8, t_(2g)^(2,2,2)e_g^(1,1)implies sp^3d^2`
n=2, paramagnetic & octahedral complex