Consider following reaction: $Mg(s)+2HCl(aq)\rightarrow H_2(g)+MgCl_2(aq)$.The rate of this reaction increases when more magnesium is added.This change is due to

Question

$\begin{array}{1 1}(a)\;adding\;of\;catalyst\\(b)\;increase\;in\;surface\;area\\(c)\;change\;in\;nature\;of\;reactants\\(d)\;increase\;in\;concentration\;of\;reactants\end{array}$