In which molecule does carbon express its LOWEST oxidation number: #"methane, ethane, carbon monoxide, carbon dioxide?"#
In methane we have..............
For carbon dioxide,
In each case, the sum of the oxidation numbers equals the charge on the species, and of course we may have a neutral molecule.
As always, to assign oxidation state, we distribute the charge to the MOST electronegative atom. When we assign oxidation numbers to carbon compounds (which is an unusual exercise), we assume that the
And thus we speak of carbon oxidation:
And for ethane,