**Explanation:**

Vidyasagar, also known as Iswar Chandra Vidyasagar, was a prominent social reformer and educator in 19th century India. He played a significant role in advocating for women's rights and worked towards improving their social status.

**Hindu Widow Remarriage Act:**

One of Vidyasagar's notable achievements was his contribution to the passing of the Hindu Widow Remarriage Act. This act aimed to address the issue of the social stigma and hardships faced by Hindu widows who were not allowed to remarry. It provided legal recognition and support for widow remarriage in Hindu society.

**Timeline and Details:**

The correct answer to the given question is option 'B' (1856). The Hindu Widow Remarriage Act was indeed passed in 1856. Here is a breakdown of the timeline and details surrounding the act:

1. **Background:** In traditional Hindu society, widows were often treated as social outcasts, subjected to various restrictions, and denied the right to remarry. This practice was deeply ingrained in societal norms and had severe consequences for widows, particularly in terms of social ostracization, economic difficulties, and emotional distress.

2. **Vidyasagar's Efforts:** Vidyasagar, recognizing the injustice and suffering faced by widows, campaigned tirelessly for widow remarriage rights. He believed that denying widows the opportunity to remarry was a violation of their basic human rights and contributed to their overall degradation.

3. **Public Awareness and Advocacy:** Vidyasagar used his position as the principal of Sanskrit College in Calcutta (now Kolkata) to raise awareness about the issue. He wrote extensively on widow remarriage and the need for social reform, publishing influential works such as "Barna Parichay" and "Bidhaba Bibaha," which highlighted the plight of widows.

4. **Lobbying for Legislative Change:** Vidyasagar's activism and writings gained significant public support and brought attention to the need for legal reforms. He actively lobbied the British colonial government, which held legislative power in India at the time, to pass a law that would legalize widow remarriage among Hindus.

5. **Passing of the Act:** Vidyasagar's efforts bore fruit when the Hindu Widow Remarriage Act was finally passed in 1856. The act allowed Hindu widows to remarry, provided certain conditions were met. It aimed to remove the stigma associated with widowhood and give widows the opportunity to lead a dignified life.

6. **Impact and Significance:** The passing of the act was a significant milestone in the women's rights movement in India. It challenged deeply entrenched social norms and paved the way for future reforms aimed at improving the status and rights of women in Indian society.

In conclusion, Vidyasagar's relentless efforts and advocacy for widow remarriage rights led to the passing of the Hindu Widow Remarriage Act in 1856. This act played a crucial role in addressing the social stigma faced by Hindu widows and granting them the legal right to remarry.

A