What happens when:
$(i)$ Concentrated $H_2SO_4$ is added to calcium fluoride
$(ii)$ $SO_3$ is passed through water?

(N/A) $(i)$ When concentrated $H_2SO_4$ is added to calcium fluoride $(CaF_2)$,it undergoes a double displacement reaction to form calcium sulfate and hydrogen fluoride gas:
$CaF_2 + H_2SO_4 \rightarrow CaSO_4 + 2HF$
$(ii)$ When $SO_3$ is passed through water,it reacts to form sulfuric acid $(H_2SO_4)$:
$SO_3 + H_2O \rightarrow H_2SO_4$