Which of the following has the greatest reducing power?

Oxyacids of chlorine show similarity in

The least active halogen with hydrogen is

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

Which of the following is most stable towards heat?

Like other halogens,fluorine cannot exhibit higher oxidation states. The reason for this is ...