Answer : 3. "sixth"
Explanation :

1. The membership of the Rajasthan Legislative Assembly, as determined by the Delimitation Commission, was 160 in 1952 and at present is 200 after considerable recommendations of the same Commission.

2. The first Rajasthan Legislative Assembly (1952-57) was inaugurated on 31 March 1952.

3. It had 160 members. It was increased to 190 after the merger of the then Ajmer state with Rajasthan in 1956.

4. The number in the second (1957–62) and third (1962–67) assemblies was 176. The fourth (1967–72) and fifth (1972–77) Legislative Assemblies had 184 members.

5. Increased to 200 from the sixth Legislative Assembly (1977–80).