Answer : 1. "1875"
Explanation :

1. Arya Samaj is a monotheistic Hindu reform movement in India that promotes principles and practices based on belief in the infallible authority of the Vedas.

2. Maharishi Dayanand Saraswati founded the society on April 10, 1875.

3. Arya Samaj follows the belief that there is only one God and his idol worship is not appropriate.

4. Arya Samaj was the first Hindu organization to promote proselytism.