As an element, oxygen is a gas. explain how oxygen can be most common element in earth’s crust, yet earth’s crust is not a gas.

1.40 moles of O₂, and 2.80 moles of NO₂

Explanation:

The balanced reaction of nitrogen monoxide (NO) with oxygen (O₂) is:

2NO(g) + O₂(g) → 2NO₂(g)

We can notice that the stoichiometry is 2 moles of NO: 1 mole of O₂: 2 moles of NO₂, thus, for 2.80 mol of NO:

2 moles of NO 1 mol of O₂

2.80 moles       x

By a simple direct three rule:

2x = 2.80

x = 1.40 moles of O₂

2 moles of NO 2 moles of NO₂

2.80 moles       y

By a simple direct three rule:

y = 2.80 moles of NO₂.