Explanation:

All statements are correct.

• Dr. B.R. Ambedkar was born in 1891 in Mhow, Central Province (now Madhya Pradesh).
• He is known as the Father of the Indian Constitution and was India's first Law Minister.
• He was the Chairman of the Drafting Committee for the new Constitution. 
• He participated in all three Round Table Conferences.
• In 1932 Dr. Ambedkar signed the Poona pact with Mahatma Gandhi, which abandoned the idea of separate electorates for the depressed classes (Communal Award).
• However, the seats reserved for the depressed classes were increased from 71 to 147 in provincial legislatures and to 18% of the total in the Central Legislature. 

He wrote many books like,

• Annihilation of Caste,
• Buddha or Karl Marx,
• The Untouchable: Who are They and Why They Have Become, Untouchables,
• Buddha and His Dhamma,
• The Rise and Fall of Hindu Women. 

Hence option 4th is correct.