Step 1: Background of Bharatiya Jana Sangh
- The Bharatiya Jana Sangh (BJS) was founded in 1951 by Syama Prasad Mukherjee.
- It was the political arm of the Rashtriya Swayamsevak Sangh (RSS).
- Its ideology was based on cultural nationalism, promoting the idea of unity through a single national identity.
Step 2: Understanding the slogan
- The idea of “one country, one culture, and one nation” reflected the belief that India’s unity could be preserved by emphasizing cultural integration.
- The Bharatiya Jana Sangh rejected divisions based on caste, community, or regional identity, and stressed national integrity.
Step 3: Analyzing the options
- (A) Socialist Party: Focused on social and economic equality, not this slogan.
- (B) Bharatiya Jana Sangh: Correct, it strongly advocated the idea of one nation and cultural unity.
- (C) Indian National Congress: Advocated secularism and pluralism, not this cultural slogan.
- (D) None of these: Incorrect, since the right answer is already (B).
Step 4: Conclusion
Thus, the Bharatiya Jana Sangh emphasized on the idea of “one country, one culture, and one nation.”
\[
\boxed{\text{Correct Answer: (B) Bharatiya Jana Sangh}}
\]