The correct answer is option 3: his account of commercial, religious, and social conditions in the East. Marco Polo`s journey to India in 1271 gained a lot of fame in Europe due to the detailed and fascinating account he provided about the trade, religion, and society in the East. His book, "The Travels of Marco Polo," was widely read and contributed to Europeans` understanding of the rich and diverse cultures of the Far East.

Option 1 states that Marco Polo discovered a safe route to India, but this is not accurate. Marco Polo`s journey did not involve discovering a new route to India; rather, he travelled along the established Silk Road and visited various regions in Asia.

Option 2 suggests that Marco Polo established friendly relations with many Kings of India, but this is not entirely true. Although Marco Polo did interact with several rulers during his travels, such as Kublai Khan in China, there is no specific mention of him establishing strong connections with Indian kings.

Therefore, option 3 is the most accurate choice as it highlights the main reason for Marco Polo`s fame in Europe - his detailed account of the commercial, religious, and social conditions in the East.