Dropping a subject. Should I?

Chemistry is more or less irrelevant to your chosen course, and you are only required to take 3 A-levels for entry into such courses. So there is absolutely no reason not to drop it, and there may be some reason to drop it - namely that if you do, you can focus on your main subjects more.

If you're considering Computer Science, you may want to consider picking up AS or A-level Further Maths if it's available to you however.

Oh okay. In my case then it would be better to drop as I am struggling through it as you mentioned, it won't need for my course later. Nope there is no option for Further Maths in my country, Nepal. Would that still be fine without it and dropping Chemistry? However I do have Computer Science so i guess it will take some advantages while applying.But I am still worried about Chem in the decission of dropping.
And what about General Paper, it is a complusory subject in which we have to write an eassy. Will Gp grades count or considered while applying?

Not taking Chemistry won't make a difference - only three A-levels are required for degrees in the UK, including Maths. Just focus on getting the best grades you can in your other subjects (especially Maths!)

The general paper will normally not form part of any offer and won't be considered, in line with General Studies and Critical Thinking from UK students - some universities use them as "tie breakers" but increasingly they're just not factored in at all. So don't worry too much about that either.