(a) Define catalyst.

(b) What are (i) positive catalysts and (ii) negative catalysts? Support your answer with one example for each of them.

(c) Name three biochemical catalysts found in the human body.

(a) A catalyst is a substance that either increases or decreases the rate of a chemical reaction without itself undergoing any chemical change during the reaction.

(b) Positive Catalyst — When a catalyst increases the rate of a chemical reaction, it is known as a positive catalyst.
For example, Finely divided iron is used as a positive catalyst in the manufacture of ammonia from hydrogen and oxygen.

$\text{N}$2 + 3\text{H}2 \xrightleftharpoons[\text{200-900 atmos.}]{\text{Fe catalyst/450\degree C }} \text{2NH}_3

Negative Catalyst — When a catalyst decreases the rate of a chemical reaction, it is known as a negative catalyst.
For example, Phosphoric acid acts as a negative catalyst to decrease the rate of decomposition of hydrogen peroxide.

(c) The three biochemical catalysts found in the human body are amylase, trypsin, pepsin.