As the atomic number of halogens increases,the halogens

Which of the following statements is correct?

Which of the following decreases down the halogen group?

Write balanced chemical equations for the following:
$(i)$ $NaCl$ is heated with concentrated sulphuric acid $(H_{2}SO_{4})$ in the presence of manganese dioxide $(MnO_{2})$.
$(ii)$ Chlorine gas $(Cl_{2})$ is passed into an aqueous solution of sodium iodide $(NaI)$.

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

Chlorine dioxide is best prepared by passing dry: