An example of a Lewis acid is

The values of dissociation constants $(K_a)$ of some acids (at $25\,^{\circ}C$) are as follows. Indicate which is the strongest acid in water:
$(A)$ $1.4 \times 10^{-2}$
$(B)$ $1.6 \times 10^{-4}$
$(C)$ $4.4 \times 10^{-10}$
$(D)$ $4.3 \times 10^{-7}$

What is the nature of an aqueous solution of ammonia?

Which gas should not be collected over water because of its high solubility in water?

Which one of the following is not a base?

Identify the conjugate acid and conjugate base for the $HCO_3{ }^{-}$ ion,respectively.