Who was the Chairperson of the 20th Law Commission of India (as of May 2013)?

The correct choice is: “Justice D.K. Jain”

The 20th Law Commission of India was constituted for 2012–2015. Justice D.K. Jain, who retired as a Supreme Court judge in January 2013, was appointed its Chairman and held the post in May 2013. He was later succeeded by Justice A.P. Shah.

“Justice P.V. Reddy” (Reddi) chaired the 19th Law Commission (2009–2012), and “Justice A.R. Lakshmanan” chaired the 18th (2006–2009). “Justice Altmas Kabir” was the Chief Justice of India at the time, not Law Commission chairman.