Atom As dalam senyawa H3AsO4 mempunyai bilangan oksidasi …

H3 As O4
+3 As -8 = 0

As = +5
H= +1
O = -2

teriamksih

Bilangan oksidasi senyawa = 0
maka
biloks H + Biloks As + Biloks O =0
Biloks H = +1, tapi karena ada 3 jadinya +3
Biloks O = -2, tapi karena ada 4 jadinya -8
sehingga Biloks As = -(biloks H)-(Biloks O)
Biloks As = -(+3)-(-8)
Biloks As = -3 + 8 =5