Which of the following orders is not true for $HClO < HClO_2 < HClO_3 < HClO_4$?

In halogens,with the increase of atomic number,which trend is observed?

Given below are two statements: one is labelled as Assertion $A$ and the other is labelled as Reason $R$.
Assertion $A :$ Fluorine forms one oxoacid.
Reason $R :$ Fluorine has the smallest size amongst all halogens and is highly electronegative.
In the light of the above statements,choose the most appropriate answer from the options given below.

The solubility of iodine in water increases in the presence of

The $pK_a$ of oxoacids of chlorine in water follows the order

Which among the following hydrogen halides is thermally least stable?