What is the specific site on an enzyme molecule where the substrate binds during a reaction called?

What binds to the active site of an enzyme?

The figure given below shows the conversion of a substrate into product by an enzyme. In which one of the four options $(A-D)$ are the components of the reaction labeled as $A, B, C,$ and $D$ identified correctly?

Match the types of enzymes in Column-$I$ with examples in Column-$II$ and select the correct option.

Column $I$	Column $II$
$i$. Purely proteinaceous enzyme	$a$. Glucokinase
$ii$. Conjugated enzyme	$b$. Epimerase
$iii$. Transferase enzyme	$c$. Protease
$iv$. Isomerase enzyme	$d$. $FMN$

The first enzyme to be isolated in crystalline form was .........

The presence of proteins in the protoplasm is of great importance because ......