Identify a species which is not a Bronsted acid but a Lewis acid.

Which of the following species acts as a base,according to the Bronsted-Lowry theory?
$HCl + NH_3 \rightleftharpoons NH_4^+{_{\text{(aq)}}} + Cl^-{_{\text{(aq)}}}$

Which one of the following species acts as both Bronsted acid and base?

According to the Lewis concept,which one of the following is not a base?

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:
$(A)$ $1.4 \times 10^{-2}$
$(B)$ $1.6 \times 10^{-4}$
$(C)$ $4.4 \times 10^{-10}$
$(D)$ $4.3 \times 10^{-7}$

In $NH_3$ and $PH_3$,the common property is