Question

What is the oxidation number of phosphorus (P) in sodium phosphate (Na3PO4)?

Answer 1

Na⁺¹₃P⁺⁵O⁻²₄

+1*3 + (+5) + (-2*4) = 0

Answer 2

Let the oxidation number of P be x.  

We know that oxidation number of Na= +1, O= -2  

therefore,  3*1 + x+ 4* -2 = 0 (net charge on the molecule)  

3 + x - 8 =0  

x = +5  

therefore, the answer is C)+5