Explanation:

- In the Union Budget 2021-22, a proposal was made under the Jal Jeevan Mission (Urban) to address the issue of liquid waste management in certain cities.

- Correct Answer: 500 AMRUT cities.

- AMRUT stands for Atal Mission for Rejuvenation and Urban Transformation, which is a government initiative aimed at ensuring robust urban infrastructure.

- The Jal Jeevan Mission (Urban) is an initiative that targets urban areas with the objective of providing universal coverage of water supply and comprehensive sewerage and septage management.

- The figure of 500 cities is significant as it highlights the government's focused approach towards improving urban infrastructure especially in the realm of waste management.

- The other options (1150, 2400, 3500, and 4350) do not relate accurately to this initiative in the context of the Union Budget 2021-22's stated goals for liquid waste management.