Which one is correct?
The bonding powder that any adhesive has depends on both its cohesion...
1) and that it adheres the surface to which it is applied
2) and its adheres to the surface to which it is applied to
3) and that it adheres to the surface which it is applied to
4) as well as its adherence to the surface to which it is applied
I know about the parallelism after the word 'and' but is that okay with 'as well as' ? I believe #4 is correct but the answer key indicates #2. I'm a little mixed up!
No wonder you are mixed-up. The question is poorly written - probably by a non-native speaker of English.
Answer 2 is definitely incorrect.
Answer 4 is the closest to being correct among the options offered.