Why was the division of India into two countries difficult to implement?

Resistance from some political leaders.

Difficulties associated with the Religious basis of Partition:

To begin with, Muslim-majority areas in British India were not confined to a single belt. They were divided into two distinct regions, one in the west and another in the east.
Furthermore, it is important to note that not all Muslim-majority regions expressed a desire to be a part of Pakistan. Khan Abdul Ghaffar Khan, widely known as the 'Frontier Gandhi', strongly opposed the concept of a separate nation based on religious lines.
Another challenge arose from the fact that the two provinces with a significant Muslim population, Punjab and Bengal, also had substantial areas where non-Muslims formed the majority.
Additionally, there were major concerns regarding the minority communities residing on both sides of the newly drawn border. Large numbers of Hindus and Sikhs in the regions now part of Pakistan, and an equally sizable population of Muslims in Indian Punjab, Bengal, and to some extent Delhi and its surrounding areas found themselves trapped and displaced.

The British government was in favour of dividing India on a religious basis. Also, West Punjab and East Bengal were regions of Muslim majority. Thus 'Option B- Resistance from political leaders' is the correct answer. Leaders from Congress and other leaders like Gandhiji and Khan Abdul Ghaffar Khan opposed partition.