Step 1: Analyze each compound - Compound 1 (−OCH3 group attached): The −OCH3 group exhibits both inductive (−I) and mesomeric (+M) effects. However, hyperconjugation is not applicable here. Not included.
Step 2: Final Count From the analysis, only 4 compounds exhibit all three effects: inductive, mesomeric, and hyperconjugation.
Final Answer: 4.
Relative stability of the contributing structures is :