Step 1: Understanding Universal Adult Franchise
- Universal Adult Franchise means that every adult citizen, regardless of gender, caste, class, education, or wealth, has the right to vote.
- In India, this principle became the foundation of the electoral system after the adoption of the Constitution in 1950.
Step 2: First application in India
- Even before the Constitution of India came into effect, Manipur became the first part of India where elections were conducted under the principle of Universal Adult Franchise.
- This took place in June 1948 for the Manipur Legislative Assembly.
Step 3: Analyzing the options
- Assam: Did not hold such elections in 1948.
- Manipur: Correct, elections under Universal Adult Franchise were held here in June 1948.
- Sikkim: Was not yet part of India in 1948.
- Punjab: Elections here took place later, under the framework of the Indian Constitution.
Step 4: Conclusion
Thus, the first part of India where elections were held on the principle of Universal Adult Franchise was Manipur in 1948.
\[
\boxed{\text{Correct Answer: (B) Manipur}}
\]