Jason combines the two intermediate steps shown.

2 equations. First: upper N subscript 2 (g) plus upper O subscript 2 (g) right arrow 2 upper N upper O (g). Second: 2 upper N upper O (g) plus upper O subscript 2 (g) right arrow 2 upper N upper O subscript 2 (g).

Which best describes what Jason should do with the oxygen molecules?
Place two of them as products.
Place two of them as reactants.
Cancel them out because there is one in each equation.
Double them because there is one in each equation.

Place two of them as reactants.

Explanation:

In order to have a clearer view of the reaction, let us write it down in the chemical symbols so that it can make more sense.

Reaction 1

N2(g) + O2(g)> 2NO

Reaction 2

2 NO(g) + O2(g) > 2NO2(g)

Overall reaction;

N2(g) + 2O2(g) > 2NO2(g)

Hence we can see that the overall reaction involves two elementary reactions. Remember that in a sequence of nonelementary reactions, the overall reaction is the sum of all the steps in the reaction sequence. Species can only cancel out when they occur on opposite sides of the reaction equation.

In this case, oxygen occurs on the reactants side in both reaction equations, hence in then overall reaction equation, it must also occur on the reactants side bearing the correct stoichiometric coefficient to show the number of oxygen moles of oxygen participating in the overall reaction equation.

a electronegativity decreases beacuse the size of nucleus is bigger.