Calculate the oxidation number of P in {H_3}P{O_3}

To calculate the oxidation number of phosphorus (P) in {H3}PO3 (phosphorous acid), you can follow these steps:

Start with the known oxidation numbers of other elements:

Hydrogen (H) typically has an oxidation number of +1 in compounds.
Oxygen (O) typically has an oxidation number of -2 in compounds, except in peroxides (-1) or when bonded to fluorine (+2).
Phosphorous acid ({H3}PO3) is a neutral compound, so the sum of the oxidation numbers of all its elements should equal zero.

Let x be the oxidation number of phosphorus (P). In {H3}PO3, there are three hydrogen atoms (H) and three oxygen atoms (O). So, you can set up the equation:

3(H) + x(P) + 3(O) = 0

Now, substitute the oxidation numbers of hydrogen and oxygen:

3(+1) + x + 3(-2) = 0

Solve for x:

3 + x - 6 = 0

Combine like terms:

x - 3 = 0

Add 3 to both sides of the equation:

x = 3

So, the oxidation number of phosphorus (P) in {H3}PO3 is +3.