Which of the following is the correct increasing order of the reducing power of halide ions?

When chlorine gas is passed through an aqueous solution of a potassium halide in the presence of chloroform,a violet colouration is obtained. On passing more of chlorine water,the violet colour disappears and the solution becomes colourless. This test confirms the presence of ........... in the aqueous solution.

Select the correct set of species which cannot react with water but react with $NaOH$:
$(i) \, NO_2$ $(ii) \, P_4$ $(iii) \, Al$ $(iv) \, I_2$

State the electronic configurations of Group-$17$ elements.

Sea is the greatest source of some halogens. Comment.

Which element from the following combines with hydrogen to form a compound having the lowest acidic strength?