Final answer:
The oxidation number of phosphorus in ammonium hydrogen phosphite is +3. This is determined by considering the charges and oxidation states of the other atoms in the compound and ensuring the overall charge balances.
Step-by-step explanation:
To find the oxidation number of phosphorus in ammonium hydrogen phosphite, we need to consider the oxidation numbers of the other elements in the compound and apply the rules for oxidation states. Ammonium (NH4+) has a nitrogen with an oxidation number of -3 and four hydrogens each with an oxidation number of +1, summing to +1 for the whole ammonium ion. Hydrogen phosphite (HPO32-) has one hydrogen with an oxidation number of +1, and oxygen is typically assigned an oxidation number of -2 in compounds (except in peroxides). Because the hydrogen phosphite ion has a charge of -2, and oxygen contributes a total of -6 (3 atoms × -2), the hydrogen adds +1, the overall charge must balance with the oxidation number of phosphorus. To find the phosphorus oxidation number, we use the equation: oxidation state of P + 3(× -2) + 1 = -2, which simplifies to oxidation state of P - 5 = -2, leading to an oxidation number of +3 for phosphorus. Thus, the oxidation number of phosphorus in ammonium hydrogen phosphite is +3.