Question

Hina is more intelligent of the two girls. it is a comparative degree , why than is not used here can you help me?​

Answer 1

If you use 'than' , then the sentence changes as

Hina is more intelligent than the other girl, of the two girls.

You just need to understand the sentence and change the degree without changing the meaning of the sentence

Answer 2

The cooperative form of much is more
and superlative is most

See ,
Much ➡ More ➡ Most .

Here the comparison is done on one girl to the two others girls .

If the comparison will be for one to one then we will use " than" but not for two .