The nitrating mixture contains concentrated $H_2SO_4$ and concentrated $HNO_3$. In this mixture,$HNO_3$ acts as a:

The pair of compounds which cannot exist together in aqueous solution is:
$I.$ $NaH_2PO_4$ and $NaHCO_3$
$II.$ $Na_2CO_3$ and $NaHCO_3$
$III.$ $NaOH$ and $NaH_2PO_2$
$IV.$ $NaHCO_3$ and $NaOH$

According to the $Br\text{\o}nsted$ theory,which are the acids in the following reaction?
$NH_3 + H_2O \rightleftharpoons NH_4^+ + OH^-$

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

Which of the following species is an acid and also a conjugate base of another acid?

Discuss the factors affecting acid strength with examples.