Question: Which is the stronger acid in the given pairs?

1) HCLO3 and HBrO3

2)HCLO2 and HCLO

3)H2Se and H2S

My work:

1) given that the # of oxygens is the same, the most electronegative atom should result in a stronger acid, thus HCLO3 is stronger

2) HCLO2 is stronger since it has more oxygen atoms

3) Here's where my logic fails, since the structure is the same(both have 2 H+) then it boils down to 2 things to account for: electronegativity and the size of the atom. Going with electronegativity, Sulfur is more e-negative thus stronger acid  which was my original answer. BUT, the correct answer is H2SE is the stronger acid which implies in this case atomic size(Selenium is larger than Sulfur) outweighs electronegativity. I dont understand why in this case H2Se is stronger than H2S given Sulfur is more electronegative, and most importantly why the same logic used in 1) cant be applied here and how do I discern where to account for atomic size specifically or when to account for electronegativity?

Any detailed-dumbed down explanations  on the logic are highly appreciated