Which of the following is known as the hydronium ion?

What is the conjugate base of $OH^{-}$?

In the equilibrium $CH_3COOH + HF \rightleftharpoons CH_3COOH_2^+ + F^{-}$,which of the following statements is correct?

In the reaction $HCl + HF \rightleftharpoons H_2Cl^+ + F^-$,the behavior of the compound $HCl$ is......

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?

$A$ substance containing hydrogen and releasing $H^{+}$ in aqueous medium is an acid. Identify the theory suggesting this concept from the following.