Which of the following is an example of a Lewis acid?

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:

In the reaction where $HNO_3$ acts as a base,which of the following acts as the strongest acid?

Which acid is not an Arrhenius acid?

Cis-butene dioic acid $\overset{K_{a_1}(-H^+)}{\longleftrightarrow} X_1^- \overset{K_{a_2}(-H^+)}{\longleftrightarrow} X_2^{2-}$
Trans-butene dioic acid $\overset{K'_{a_1}(-H^+)}{\longleftrightarrow} Y_1^- \overset{K'_{a_2}(-H^+)}{\longleftrightarrow} Y_2^{2-}$
The incorrect statement regarding the above information is:

The conjugate base of sulphuric acid is