The reactive species in chlorine bleach is

Which among the following is the most reactive?

When a mixture of solid $NaCl$ and solid $K_2Cr_2O_7$ is heated with concentrated $H_2SO_4$,orange-red vapours are evolved. These vapours are of which compound?

Only iodine forms hepta-fluoride $IF_7$,but chlorine and bromine give penta-fluorides. The reason for this is:

Draw the molecular formula and structure of perbromic acid.

Which of the following is the strongest oxidizing agent?