One mole of alkene $\underline {X}$ on ozonolysis gave one mole of acetaldehyde and one mole of acetone. The IUPAC name of $\underline{X}$ is :

Question

$$\begin {array} {1 1} (1)\;2-Methyl-2-butene & \quad (2)\;2-Methyl-l-butene \\ (3)\;2-Butene & \quad (4)\;1-Butene \end {array}$$