In the compound Ni2O3, nickel's oxidation number is oxidation number is -2.
and oxygen's

+3

Explanation:

The name of this compound would be nickel (III) oxide. Oxygen typically has a charge of -2. Given there are 3 oxygen atoms, that would equal a charge of -6. The nickel is the cation and must equal the charge of the anion, so must have a charge of +6. Since there are 2 nickel atoms, the charge on each must be +3.

A catalyst speeds up a reaction by lowering the activation energy.

Explanation:

A catalyst has no effect on the equilibrium of a reaction.A catalyst does not add energy to a reaction neither does a catalyst consumed in a chemical reaction .

Therefore, A catalyst speeds up a reaction by lowering the activation energy.