Question

What are oxidation numbers of the elements in the compound `Na_3PO_3`?

Answer 1

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Explanation:

The compound is neutral, meaning that the oxidation numbers will cancel each other out:
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Na in a compound is pretty much always +1

Hence, we have `3*(+1)` coming from the 3 Sodiums
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Oxygen unless in an elemental or peroxide form will have an oxidation number of -2

Hence, we have `3*(-2)` coming from the 3 Oxygen atoms
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Because the compound is neutral we know that

`+3_(f rom Na)-6_(f rom O)+P=0`
`P=+3`

Therefore
Na (+1)
P (+3)
O (-2)