Let $G$ be a connected compact simple Lie group of one of the following types: $A_l$, $B_l$, $C_l$, $D_l$, $E_6$, $E_7$, $E_8$, $F_4$, $G_2$. Which one of these admit an irreducible faithful representation?
Links that might help:
Lowest-dimensional faithful representations of compact Lie groups