* CO (Carbon Monoxide): CO has a linear shape. While carbon and oxygen have different electronegativities, the linear geometry means the polarities cancel out, making it non-polar.

* SO2 (Sulfur Dioxide): SO2 has a bent shape due to the lone pair of electrons on sulfur. This bent shape results in a net dipole moment, making it polar.

* NO (Nitrogen Monoxide): NO has an odd number of electrons and a bent shape due to the lone electron on nitrogen. This makes it polar.

* AlCl3 (Aluminum Chloride): AlCl3 has a trigonal planar geometry. Although aluminum and chlorine have different electronegativities, the symmetrical shape results in the polarities canceling out, making it non-polar.

Therefore, the non-polar molecules are CO and AlCl3.