What is the chemical formula (ll) hydroxide

Ni(OH)2 is the formula. Or in another view H2NiO2 meaning that you will need...

Hydrogen molecules=2
Nickel and oxygen molecules=2

Hope this helped. :)

The problem here is that according to aufbau principle before 3d orbital 4s subshell comes.after filling 3p orbital with electrons you have 4 electrons left, you place two in 4s with opposite spin and the other two in 3d in any of its two orbitals of total five orbitals with the same spin.