Which of the following salts is acidic?

Match the following:

List-$I$ (Acid)	List-$II$ ($K_a$ - Ionization Constant)
$A$. $HCN$	$I$. $6.8 \times 10^{-4}$
$B$. $H_2C_2O_4$	$II$. $8.9 \times 10^{-8}$
$C$. $H_2S$	$III$. $4.9 \times 10^{-10}$
$D$. Niacin	$IV$. $5.6 \times 10^{-2}$
	$V$. $1.5 \times 10^{-5}$

The correct match is:

$A$ $Lewis$ acid is defined as a substance that acts as a:

Complete the following Acid-Base reactions and identify each reactant as an Acid or a Base:
$(i)$ $CH_3NH_2 + H_2O$
$(ii)$ $CO_2 + H_2O$
$(iii)$ $H_2PO_4^- + CO_3^{2-}$
$(iv)$ $NH_2NH_2 + H_2O$
$(v)$ $C_6H_6 + NO_2^+$
$(vi)$ $C_6H_6 + NH_2^-$

Which of the following oxides will not give $OH^{-}$ ions in aqueous solution?

When $KHSO_4$ is added into a concentrated solution of $H_2SO_4$,the acidity of the solution