What is the oxidation number for CO2

+4

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].