Answer:
Double bond
Explanation:
Carbon is a tetravalent atom. This implies that the carbon atom always forms four covalent bonds.
These four covalent bonds may be single, double or triple bonds. Compounds that contain double and triple bonds are said to be "unsaturated".
If the last carbon atom of an unsaturated fatty acid is bonded to two hydrogen atoms and one carbon atom, it means that the bond between the last carbon and the other carbon atom must be a double bond because carbon must be tetravalent and we have already been told that the fatty acid is unsaturated.
The last carbon atom of the unsaturated fatty acid must form two covalent bonds to the other carbon atom in order to respect the tetravalency of carbon.
