103. Assign oxidation number of the underlined elements in each of the following species:

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Let the oxidation number of P = x
Writing the oxidation number of each atom at the top of its symbol.
                 +1 + 1 x - 2
                 Na  H₂PO₄    
Sum of the oxidation number of various atoms = 0
                                +1+2(+1)+x+4(-2) = 0
                                        x - 5 = 0
or                                      x = 5
  Oxidation number of P in NaH₂PO₄ = 5