what problem will i am going to face if in bsc if base of my 11th and 12th is not clear
Hello, I hope you are doing well
The answer to this question actually depends on how much hard work are you are willing to do .
If you do not have a solid foundation of basics, then yes you will struggle at some points during the B.Sc. such as if your concept and understanding of calculus is not good, undergraduate degree will be a tough one for you to deal with.
But, even if you think you do not have a clear concept its okay. You will just have to work somewhat harder than rest of your mates, you will have plenty of time during your course to clear all of the concepts, assuming that you are willing to work towards that.
Hope this helps