The correct answer is option 1, "Those who immersed in devotion to Vishnu." Alvars were a group of poet-saints who lived between the 6th and 9th centuries in South India. They were considered to be the forerunners of the Bhakti movement, which emphasized intense personal devotion to a particular deity. The Alvars were known for their unwavering love and devotion to Lord Vishnu, especially his various incarnations such as Rama and Krishna.

Option 2, "Devotees of Shiva," is incorrect as the Alvars focused their devotion specifically on Lord Vishnu and his incarnations. Option 3, "Those who worshipped abstract form of God," is also incorrect as the Alvars had a personal and emotional connection with Lord Vishnu rather than an abstract concept. Option 4, "Devotees of Shakti," is unrelated to the Alvars, as they were predominantly devoted to Lord Vishnu.