What change did the forty-second amendment make to the duration of legislatures in India?

Extended it from five to six years

The correct answer is Option 4- Extended it from five to six years 

The forty-second amendment extended the duration of legislatures in the country from five to six years.

The Parliament also brought in many new changes to the Constitution. In the background of the ruling of the Allahabad High Court in the Indira Gandhi case, an amendment was made declaring that elections of Prime Minister, President and Vice- President could not be challenged in the Court. The forty-second amendment was also passed during the Emergency. This amendment consisted of a series of changes in many parts of the Constitution. Among the various changes made by this amendment, one was that the duration of the legislatures in the country was extended from five to six years. This change was not only for the Emergency period, but was intended to be of a permanent nature. Besides this, during an Emergency, elections can be postponed by one year. Thus, effectively, after 1971, elections needed to be held only in 1978; instead of 1976.