Two other ministers Swantradev Singh and Mohsin Raza also took oath.
The development came on a day Bharatiya Janata Party President Amit Shah arrived on a three-day visit to the state capital.
"Mohit Yadav is my name...," said the 24-year-old, before slapping sub-inspector Jitendra Kumar.
In the coming assembly election, negotiations over seat-sharing will be as important as actual outreach to voters.
Throughout the governor's 35-minute address, Samajwadi Party legislator Rajesh Yadav blew a whistle.
Opposition MLAs flung paper balls at Governor Ram Naik and marshals frantically deflected the projectiles with files as the opening day of the maiden session of the new Uttar Pradesh assembly presented a spectacle of complete mayhem.
About 2.34 crore voters, spread across 78 assembly segments of the 243-strong assembly, will decide the fates of 1,204 candidates, including the Speaker and 12 members of the state cabinet.
The Rajya Sabha elections in Uttar Pradesh on Saturday saw cross-voting by a BJP MLA while another party legislator claimed that she was prevented from voting.
The Rajya Sabha on Wednesday took up the four bills related to the GST, with the Opposition urging the government to insulate taxpayers from harassment and questioning how the new regime was "ideal" when 40 per cent of the revenue base of the GDP was kept out of its purview.
Here's a list of the full first-time ministers in the second term of the Narendra Modi government.