Who served as the Executive Chairperson of NALSA (National Legal Services Authority) in February 2019?

The correct choice is: “Justice A. K. Sikri”

By convention, the Executive Chairman of NALSA is the senior-most Supreme Court judge after the Chief Justice of India, who is its Patron-in-Chief. Justice Madan B. Lokur held the post until he retired on 30 December 2018. Justice A. K. Sikri succeeded him and held it until he retired on 6 March 2019, so he was Executive Chairperson in February 2019.

Justice Madan B. Lokur had retired by then, and Justices Nariman and Chandrachud were not Executive Chairpersons at that time.