Valency and oxidation number are different for an element. Valency of carbon is generally 4, however, the oxidation state may be −4,−2,0,+2,−1, etc. In the compounds containing carbon, hydrogen and oxygen, the oxidation number of carbon can be calculated as: Oxidation number of carbon=2nO−nHnC where, nH,nO and nC are number of respective atoms.
In which of the following compounds, the valency of carbon is two?