Answer 1

Mainly the fact C is a general programming language that can be compiled to run on most systems whereas Objective-C is from Apple and used for iOS & Mac. Swift has somewhat replaced that, but if the Obj-C tools are still available/maintained there's no reason people who know them well and haven't learned Swift would immediately abandon them.

Answer 2

Yes there is StudioYol
C is a general purpose programming language (procedural programming).

Objective-C is more of an high-level object-oriented programming language. (A subset of C, everything valid in C is also valid in Objective-C).