Ranking Acidity

What are the factors that affect the strength of an acid?

Rank the following in terms of acidity: HClO, HClO$_2$, HClO$_3$, HClO$_4$. Explain the trend.

Rank the following in terms of basicity:

HCN K$_a$ = 4.8 x 10$^{-10}$

HSO$_4^-$ K$_a$ = 1.2 x 10$^{-2}$

HS$^-$ K$_a$ = 7.1 x 10$^{-15}$

H$_2$CO$_3$ K$_a$ = 4.3 x 10$^{-7}$

In the below reactions, identify which reactant is the lewis acid and which is the lewis base.

NH$_3$ + BF$_3$ $\leftrightharpoons$ NH$_3$BF$_3$

KOH + CH$_3$Br $\leftrightharpoons$ KBr + CH$_3$OH