Enzymes are best defined as

Which of the following is an enzyme?

The figure shows the conversion of substrate into product by an enzyme. In which one of the four options are the components of the reaction labelled $a, b, c, \& \ d$ identified correctly?
$(i)$ Potential energy
$(ii)$ Transition state
$(iii)$ Activation energy with enzyme
$(iv)$ Activation energy without enzyme

What is the enzyme called that catalyzes the breakdown of a complex inorganic substance into simpler substances by adding a water molecule?

In the human body,which of the following requires protein for its activity?

Assertion : Allosteric enzymes show feedback inhibition.
Reason : The inhibitor is competitive.