Which of the following substituents has +M (Mesomeric) effect ?
 

Given data: It is given to identify that which substituents has +M (Mesomeric) effect.
Explanation:  When the electrons or the pi electrons are transferred from a selected group towards a conjugate system, thus increasing the electron density of the conjugated system then such a phenomenon is understood as (+M) effect or positive mesomeric effect.
 

NR₂ , - NH₂ , - NHR` groups are +M groups.

Hence, option (C) -NH₂ is correct answer.