Which of the following conversions is carried out by using a charcoal catalyst?

• A
  $SO_{2(g)} + Cl_{2(g)} \rightarrow SO_2Cl_{2(l)}$
• B
  $4HCl + O_2 \rightarrow 2Cl_2 + 2H_2O$
• C
  $2SO_{2(g)} + O_{2(g)} \rightarrow 2SO_{3(g)}$
• D
  $2ZnS_{(s)} + 3O_{2(g)} \rightarrow 2ZnO_{(s)} + 2SO_{2(g)}$