Answer
$CH_{4}$ is non-polar and has very weak dispersion forces between its molecules, whereas $SO_{2}$ is a polar molecule and has stronger dipole-dipole forces. Under the same conditions of temperature and density, $SO_{2}$ will behave less ideally as ideal gases have no attractive forces at all.
Work Step by Step
$CH_{4}$ is non-polar and has very weak dispersion forces between its molecules, whereas $SO_{2}$ is a polar molecule and has stronger dipole-dipole forces. Under the same conditions of temperature and density, $SO_{2}$ will behave less ideally as ideal gases have no attractive forces at all.
