Question

part 3 (0.3 point)
give the chemical formula of phosphoric acid;

part 4 (0.3 point)
write the chemical formula of nitrous acid;

Explanation:

Step1: Recall phosphoric acid composition

Phosphoric acid contains phosphorus (P), oxygen (O), and hydrogen (H). Phosphorus is in +5 oxidation - state in phosphoric acid, and it is bonded to four oxygen - atoms and three of the oxygen - atoms have a hydrogen atom attached to them.
The chemical formula is $H_3PO_4$.

Step2: Recall nitrous acid composition

Nitrous acid contains nitrogen (N), oxygen (O), and hydrogen (H). Nitrogen is in +3 oxidation - state in nitrous acid. It has the chemical formula $HNO_2$.

Answer:

Part 3: $H_3PO_4$
Part 4: $HNO_2$