HCI and HF are prepared by heating their salt (NaCl and CaF2) with conc. H2SO4 but HI and HBr cannot he prepared by similar reaction because HBr and HI have

H2​SO4​ acts as oxidizing agent and oxidises HI but HCl is not oxidised by  H2​SO4​.Hence, HCl is prepared by heating NaCl with conc. H2​SO4​ but HI cannot be prepared by treating NaI with conc. H2​SO4​.