Which of the following compounds exhibits a positive mesomeric effect ($+M$ effect)?

What is the difference between the mesomeric effect and the resonance effect?

Explain the terms Inductive and Electromeric effects. Which electron displacement effect explains the following correct orders of acidity of the carboxylic acids?
$(a)$ $Cl_3CCOOH > Cl_2CHCOOH > ClCH_2COOH$
$(b)$ $CH_3CH_2COOH > (CH_3)_2CHCOOH > (CH_3)_3C \cdot COOH$

Match List-$I$ with List-$II$:
| List-$I$ (Mechanism steps) | List-$II$ (Effect) |
| :--- | :--- |
| $(A)$ Aniline resonance structure | $(I)$ $-E$ effect |
| $(B)$ Electrophilic addition of $H^+$ to alkene | $(II)$ $-R$ effect |
| $(C)$ Nucleophilic addition of $CN^-$ to alkene | $(III)$ $+E$ effect |
| $(D)$ Nitrobenzene resonance structure | $(IV)$ $+R$ effect |
Choose the correct answer from the options given below:

Identify the type of electromeric effect ($E$-effect) in the following reactions:
$(a) >C=C< + CN^{-} \to -C(CN)-C^{-}-$
$(b) >C=C< + H^{+} \to -C^{+}-CH-$

In which of the following compounds is the hyperconjugation effect not present?