Question

what secondary pollutant is created by nitrogen oxides? pure oxygen nitric acid ice crystals water vapor

Explanation:

Nitrogen oxides ($NO_x$) can react with other substances in the atmosphere. For example, nitrogen dioxide ($NO_2$) can react with water vapor ($H_2O$) and oxygen ($O_2$) in the atmosphere. The chemical reaction is $4NO_2 + 2H_2O+O_2 = 4HNO_3$. Nitric acid ($HNO_3$) is a secondary pollutant formed from nitrogen oxides. Pure oxygen ($O_2$) is a natural component of the air and not formed as a secondary pollutant from nitrogen oxides in this context. Ice crystals are related to temperature and water - phase changes, not a product of nitrogen oxide reactions. Water vapor is a natural atmospheric component and not a secondary pollutant formed specifically from nitrogen oxides in the way described.

Answer:

nitric acid