Answer:
+4
Step-by-step explanation:
The oxidation number of C in carbon dioxide (CO2) is (rules 1 & 2): 0 + (2 x 2) = +4 [Check (rule 3): +4 + 2(-2) = 0] The oxidation number of C in methane (CH4) is (rules 1 & 2): 0 – (4 x1) = -4 [Check (rule 3): -4 + 4(-1) = 0].