Simplify the following text for a Grade 6 native English-speaking person.
Original: Nickel ( II ) oxide is the chemical compound with the formula NiO . It is notable as being the only well characterized oxide of nickel ( although nickel ( III ) oxide , Ni2O3 and NiO2 have been claimed ) .
Simplified: Nickel ( II ) oxide can be made by heating nickel powder in air at 400 C. This normally makes a black nickel oxide .