One mole of alkene X on ozonolysis gave one mole of acetaldehyde and one mole of acetone. The IUPAC name of X is

To find out the starting reactant from ozonolysis, place the two molecules together with carbonyl groups facing each other as shown in following figure. Then put the double bond at the place of these carbonyl groups and attach them. The given ozonolysis product has 2- methyl, but- 2-ene as starting reactant.