Hello student,

For biology or science subjects being in class 12, you may follow the following mentioned applications

1. Byjus the learning app

2. Vedantu

3. myCBSEguide (for NCERT solutions)

However a few things should be kept in mind while considering the above options. The live lectures for the 1st 2 applications are somewhat paid however the solutions in the Third application is absolutely free. If you solely want to clear some specific concept related doubts, youtube is the best platform to head over to. You can also find some online tutoring websites that provide quality teaching at a nominal cost.

I hope this helps you to a certain extent.