Which element is used as a cofactor for enzymes and as a component of human diet?

Which of the following enzymes are activated in the presence of $Mg^{++}$?
$(A)$ Pyruvate dehydrogenase
$(B)$ $DNA$ polymerase
$(C)$ Hexokinase
$(D)$ Rubisco
$(E)$ Catalase
$(F)$ $PEP$ carboxylase
$(G)$ Amylase
Options:
$(a)$ $B, C, D, E$
$(b)$ $A, F, C, D$
$(c)$ $G, F, B, E$
$(d)$ $A, F, C, B$

Small molecules compared to the protein part of enzymes are known as:

$.........$ is a cofactor for the proteolytic enzyme carboxypeptidase.

Vitamins function as .........

$A$ : Cofactor of an enzyme may be a prosthetic group.
$R$ : $NAD$ derived from niacin is a co-enzyme.