The compound $HCl$ behaves as $...$ in the reaction,$HCl + HF \to H_2Cl^{+} + F^{-}$

When a solution of $NaOH$ is left exposed to air for a few hours,what happens?

Consider the following data for a series of hydrogen halide Bronsted acids:-

Acid	$HF$	$HCl$	$HBr$	$HI$
$K_a$	$7.2 \times 10^{-4}$	$1 \times 10^6$	$1 \times 10^9$	$3 \times 10^{11}$

Which of these Bronsted acids would have the weakest conjugate base?

Arrange the anions $(p) \text{CH}_3^{-}, (q) \text{NH}_2^{-}, (r) \text{OH}^{-}, (s) \text{F}^{-}$ in decreasing order of their basic strength.

On dissolving $1 \ mole$ of each of the following acids in $1 \ L$ of water,the acid which does not give a solution of strength $1 \ N$ is:

$CH_3COOH_{(aq)} + H_2O_{(l)} \rightleftharpoons H_3O^{+}_{(aq)} + CH_3COO^{-}_{(aq)}$. Between $H_2O$ and $CH_3COO^{-}$,which one is the weaker base?