The question pertains to the sociologist credited with classifying social groups into ‘dyad’ and ‘triad’.
According to the provided options and correct answer, Franklin Henry Giddings is identified as the sociologist responsible for this classification.
Giddings, an influential American sociologist, developed theories concerning social consciousness and the nature of groups.
While Georg Simmel extensively analyzed the unique social dynamics within dyads (two-person groups) and triads (three-person groups), this question, based on the given options, points to Giddings.
Conclusion: Giddings classified groups into 'dyad' and 'triad'.
| List-I | List-II |
| a. Primary group | i. Summer, W.G. |
| b. Reference group | ii. Bierstedt, Robert |
| c. In-groups and Out-groups | iii. Hyman, R |
| d. Organised group | iv. Charles Cooley |