Best third option for A-levelWatch
Good universities see Business as a soft/easy subject and so it less alot less respected than Maths- more likely to get offers with a good grade in Maths A Level
And, Maths will seriously help with both Biology and Chemistry so I am told
But if you mean just helping you with chemistry A-level - every A-level is independent (except further maths assuming maths content) and doesn't assume knowledge from any other. My understanding is that chemistry's mathematical content is mostly plugging into formulas and using logarithms, similar to physics. The maths you cover in physics or chemistry (though I can only conclusively speak about the former since I didn't take chemistry) is pretty basic compared to that covered in A-level. If you're confident with GCSE maths, you'll be fine with the maths in A-level sciences.
You've already got two solid A-levels that'll give you a fair amount of options so it'd be fine to pick business if you prefer it.
If you went on to a degree in chemistry, then A-level Maths would be very useful (and you will probably cover at least some of that content in such a degree if you haven't already). For the biosciences it is less directly important but it should be noted that in general any scientific degree, and indeed all science beyond degree level, is going to be something of a mathematical endeavour, as mathematics is the language of the natural sciences. That shouldn't necessarily put you off but if you strongly dislike maths you may want to evaluate why it is you don't like maths but do like science, and whether you can reconcile those two things.
For something like medicine though, they don't care at all what your third subject is provided you get an A or A* in it. I still think the above applies but, since the first and possibly greatest barrier to entry in medicine is getting and then achieving an offer for the subject, you may as well focus on just taking the subject(s) you need to while otherwise maximising the odds of you getting AAA or above.
In any other subject it won't matter if A-level Maths isn't specifically required (as it is for, e.g. most economics degrees). For something like anthropology or politics they won't care whether you did maths or business at A-level.