Recall, π is defined as the ratio of the circumference (say c) of a circle to its diameter (say d). That is, π = c/d. This seems to contradict the fact that π is irrational. How will you resolve this contradiction?

π is a ratio of magnitudes, circumference/diameter, but it is not a ratio of integers. For example, √5 is an irrational number but it is expressed in a/b form. Therefore π is an irrational number. If circumference is an integer then diameter is not an integer and vice-versa.