Answer
$HNO_{2}$
Work Step by Step
Nitrite anion ($NO_{2}^{-}$) has a -1 charge. To form an acid, hydrogen ion is required to neutralize it. Hydrogen ion ($H^{+}$) has a a +1 charge. The charges are balanced, the chemical formula will be $HNO_{2}$.
In naming the compound when hydrogen ion is added, -ite is replaced by -ous and acid is added at the end. Therefore the name will be nitrous acid.
