What is the conjugate base of chloric acid?

What is meant by the conjugate acid-base pair? Find the conjugate acid/base for the following species: $HNO_2, CN^{-}, HClO_4, F^{-}, OH^{-}, CO_3^{2-}$ and $S^{2-}$

Derive the equation of the relation between the weak base ionization constant $K_b$ and its conjugate acid ionization constant $K_a$.

Which of the following are Lewis acids? $H_2O, BF_3, H^{+}, NH_4^{+}$

Match the following acids in List-$I$ with their respective acid dissociation constants $(K_a)$ in List-$II$:

List-$I$ (Acid)	List-$II$ $(K_a)$
$A$. Phenol	$I$. $1 \times 10^{-13}$
$B$. Benzoic acid	$II$. $3.0 \times 10^{-8}$
$C$. $HClO$	$III$. $1.0 \times 10^{-10}$
$D$. $CH_3COOH$	$IV$. $6.5 \times 10^{-5}$
	$V$. $1.75 \times 10^{-5}$

The correct match is:

Conjugate base for Bronsted acids $H_{2}O$ and $HF$ are