The correct option is "lot of". The phrase "lot of" is commonly used to refer to a large quantity of both countable and uncountable things.
The sentence becomes:
We saw a lot of animals at the zoo.
The correct option is "lot of".
Arun’s present age in years is 40% of Barun’s. In another few years, Arun’s age will be half of Barun’s. By what percentage will Barun’s age increase during this period?