Question
Oxidation number of P in PO43-, of S in SO42- and that of Cr in Cr2O72- are respectively,
-
+5,+6 and +6
-
+3, + 6 and +5
-
+5,+3 and +6
-
-3,+6 and +6
Solution
A.
+5,+6 and +6
(i) Sum of oxidation states of all atoms = charge of ion.
(ii) oxidation number of oxygen = -2
Let the oxidation state of P in PO43- is x.
PO43-
x + 4 (-2) = - 3
x-8 = - 3
x = +5
Let the oxidation state of S in SO42- is y
y + 4(-2) = -2
y-8 = - 2
y = +6
Let the oxidation state of Cr in Cr2O72- is z.
2 x z+7(-2) = -2
2z-14 = - 2
z=+6
Hence, oxidation state of P, S and Cr are +5, +6 and +6
