A -> If you're referring to someone else's purple bow, you would say "yours." Not "your's."
B -> "Theirs" is gramatically incorrect. You would just say "their."
C -> "It's" is used in the wrong way. You would just say "its rightful owner." "It's" refers to "it is" & if you plug that into the sentence, it makes no sense.
You can take physics as a hobby and also it is gre that you like both maths and physics as well and also want to be an computer science engineer because physics and math.
