Step 1: Understanding the question:
The question asks which sociologist introduced the term 'Sanskritisation' into Indian sociology.
Step 2: Key fact:
M. N. Srinivas coined the term Sanskritisation in his study of the Coorgs of South India, to describe the process by which a lower or middle caste (or tribal group) takes over the customs, rituals, beliefs and lifestyle of an upper/'twice-born' caste in an attempt to claim a higher position in the caste hierarchy.
Step 3: Why other options are wrong:
S. C. Dubey and D. N. Majumdar are notable Indian sociologists/anthropologists but are not credited with coining this specific term.
Final Answer:
M. N. Srinivas (option iii).