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

Which of the following species are only Lewis acids but not Bronsted acids from $CO_{2}$,$BCl_{3}$,$NH_{3}$,$CH_{3}NH_{2}$,$NO_{2}^{+}$,and $C_{6}H_{5}NH_{3}^{+}$?

The dissociation of $H_3PO_4$ occurs in how many stages?

$HSO_4^-$ is the conjugate base of

Weak acids are partially ionised in aqueous solutions. The ionisation constants of some acids are given below. Arrange these acids in increasing order of their acid strength.

Acid Index	Acid Name and Ionisation Constant $(K_a)$
$1$	Formic acid $(HCOOH)$: $1.8 \times 10^{-4}$
$2$	Hypochlorous acid $(HClO)$: $3.0 \times 10^{-8}$
$3$	Nitrous acid $(HNO_2)$: $4.5 \times 10^{-4}$
$4$	Hydrocyanic acid $(HCN)$: $4.9 \times 10^{-10}$

The self-ionization constant of $NH_3$ is $........... $.