Why is respiration considered as exothermic process?

That's a great question. Respiration is considered exothermic for a very simple reason: it releases energy.

Think of it this way. During respiration, your body breaks down complex molecules like glucose (from food) into simpler ones, carbon dioxide and water. The glucose molecule holds a great deal of chemical energy stored in its bonds. The products have far less stored energy. This difference in energy doesn't just vanish; it has to be released.

This released energy comes out in two main forms: chemical energy (ATP) that powers our cells, and heat. This very heat is what helps to maintain our constant body temperature. Because energy is given out of the system, it's a classic exothermic process.