Oxidation number of S in SO42− is :
+6
+3
+2
-2
Oxidation number (O.N.) of S in SO42−
found as :
O.N. of S+4 (O.N. of O ) =−2
O.N. of S+4(−2)=−2
O.N. of S−8=−2
O.N. of S=−2+8=+6.