The provided context includes Question 18 which asks why we apply paint on iron articles, and Question 19 which asks why oil and fat containing food items are flushed with nitrogen. These questions indicate that corrosion affects iron articles (hence painting for prevention) and rancidity affects oil/fat containing foods (hence nitrogen flushing for prevention). However, the context does not provide detailed definitions or specific examples with chemical equations for these terms. The answers are constructed from the preventive measures mentioned in the related questions.