Solution:

• The Constitutional advisor (Legal advisor) to the Constituent Assembly: B.N. Rau.
• The first elected president of The Constituent Assembly: Dr Rajendra Prasad.
• First interim chairman of the Constituent Assembly: Sachchidananda Sinha.
• Sachchidananda Sinha took the charges on 9 December 1946 but resigned on 11 December 1946.
• Dr Rajendra Prasad was elected as the first chairman of the Constituent Assembly.
• The Secretary to the Constituent Assembly: H.V.R. Iyengar.
• The chief draftsman of the constitution in the Constituent Assembly: S.N. Mukerjee.