Final answer:
None of the molecules listed (CH4, CO2, C2H6, CCl4) are optically active as they are all achiral, meaning they have symmetrical structures without chiral centers.
Step-by-step explanation:
The question asks which of the listed molecules is optically active. Optical activity is a characteristic of compounds that have the ability to rotate the plane of plane-polarized light. This property is exhibited by substances that contain chiral molecules, which means they have non-superimposable mirror images. None of the options given (CH4, CO2, C2H6, CCl4) are chiral. Methane (CH4), carbon dioxide (CO2), ethane (C2H6), and carbon tetrachloride (CCl4) are all achiral because they all have symmetrical structures and hence, no chiral centers.
Compounds like glucose, which has multiple chiral centers, are examples of optically active substances. Each chiral carbon in glucose contributes to its overall ability to rotate plane-polarized light, resulting in either dextrorotatory (d-) or levorotatory (l-) isomers.