Which of the following is a Lewis base?

Identify the conjugate acid-base pair in the following reaction: $HCl_{(aq)} + H_2O_{(l)} \rightleftharpoons H_3O_{(aq)}^{+} + Cl_{(aq)}^{-}$

The first ionization constants ($pK_a$ values) for the following dicarboxylic acids are given:
Oxalic acid: $pK_1$
Malonic acid: $pK_2$
Heptanedioic acid: $pK_3$
Which of the following represents the incorrect order of their $pK_a$ values?

The value of enthalpy of neutralization is the lowest for the reaction between:

The conjugate base of phosphorus acid is $x$. The conjugate base of oleum is $y$. What are $x$ and $y$,respectively?

$A$ $Lewis$ acid is a substance that: