Answer:
A good oxidant is the Oxygen because it has the largest electronegativity, that is 3.44
Explanation:
As the problem says an oxidant is a substance that can accept the electrons from another reagent.
There is a direct relationship between oxidizing power and electronegativity. The greater the electronegativity of an atom, the greater its oxidizing power, which means that its ability to attract electrons is greater.
For the elements given by the problem we have the following electronegativities:
O = 3.44
K = 0.98
Ni = 1.91
Therefore the element that is a good oxidant is the Oxygen because it has the largest electronegativity.