Fill in the blanks with the most appropriate option:-

Uttar Pradesh is the most ________ state of India.

populous

The most appropriate option to fill in the blanks is populous.

The word "populous" means having a large population. Uttar Pradesh is the most populous state of India, with a population of over 200 million people. The other options are not as appropriate.

• Pollution refers to the presence of harmful substances in the environment. This does not make sense in the context of the sentence, as Uttar Pradesh is not the most polluted state of India.
• Popularity refers to the state of being liked or admired by many people. This does not make sense in the context of the sentence, as Uttar Pradesh is not the most popular state of India.
• Population refers to the number of people living in a particular area. This is a more general term than "populous", and it is not the most appropriate word to use in the sentence.