Fluorine is prepared by

$HI$ cannot be prepared by the action of conc. $H_2SO_4$ on $KI$ because:

$Br_2$ gas turns starch iodide paper

Assertion : The fluorine has lower reactivity.
Reason : $F-F$ bond has low bond dissociation energy.

Which of the following reactions does not form $PCl_3$ as one of the products?

The gas evolved on heating $CaF_2$ and $SiO_2$ with concentrated $H_2SO_4$,on hydrolysis gives a white gelatinous precipitate. The precipitate is