Chapter 3, Problem 8P

Which of the following species or ions contain (a) a ${\text{C}}_3$ axis but no ${\text{σ}}_{\text{h}}$ plane, and (b) a ${\text{C}}_3$ axis and a ${\text{σ}}_{\text{h}}$ plane: ${\text{NH}}_{\text{3}}$; ${\text{SO}}_{\text{3}}$; ${\text{PBr}}_{\text{3}}$ ${\text{AlCl}}_{\text{3}}$; ${\left[{\text{SO}}_{\text{4}}\right]}^{\text{2-}}$; ${\left[{\text{NO}}_{\text{3}}\right]}^{\text{-}}$?