**Answer:**

The correct answer is option 'A' - North India.

**Explanation:**

The Arya Samaj was founded in 1875 by Swami Dayanand Saraswati in Bombay (now Mumbai). It aimed to reform and revive Hinduism, particularly in North India.

**The Arya Samaj in North India:**

1. Swami Dayanand Saraswati, the founder of the Arya Samaj, was born in Gujarat and initially started his reformist activities in the western region of India. However, he later shifted his focus to North India, particularly Punjab and Uttar Pradesh.

2. In Punjab, the Arya Samaj gained significant popularity and support, as it appealed to the Punjabi people who were seeking a reformation of their traditional religious practices.

3. The Arya Samaj established its first major center in Lahore (now in Pakistan) in 1877. Lahore became a prominent hub for the activities and growth of the Arya Samaj in North India.

4. The reformist ideas and teachings of the Arya Samaj gained traction among the educated middle class and upper-caste Hindus in North India. They were attracted to the emphasis on Vedic knowledge, rationality, and social reform.

5. The Arya Samaj actively worked towards the abolition of social evils like child marriage, caste discrimination, untouchability, and the oppression of women. It promoted education and encouraged the use of vernacular languages.

6. Swami Dayanand Saraswati traveled extensively throughout North India, delivering discourses, establishing branches of the Arya Samaj, and spreading his reformist message.

7. The Arya Samaj's influence grew rapidly in North India, and it played a significant role in shaping the religious and social landscape of the region.

8. Today, the Arya Samaj continues to have a strong presence and influence in North India, with numerous branches, educational institutions, and followers.

In summary, the Arya Samaj, founded by Swami Dayanand Saraswati in 1875, primarily undertook the task of reforming Hinduism in North India, particularly in Punjab and Uttar Pradesh. It gained popularity among the educated middle class and upper-caste Hindus and actively worked towards social reforms and the revival of Vedic knowledge.