Step 1: Understanding microwave activity.
A molecule is microwave active if it has a permanent dipole moment. Molecules that do not have a permanent dipole moment will not interact with microwave radiation.
Step 2: Analyzing the molecules.
- Trans-dichloroethene has a dipole moment due to the electronegativity difference between chlorine and carbon, making it microwave active.
- 1,2-dinitrobenzene, 3-methylphenol, and para-aminophenol either have symmetric structures or do not exhibit a permanent dipole moment.
Step 3: Conclusion.
Thus, the microwave active molecule is (A) trans-dichloroethene.