It depends, Random.Range has 2 overloaded methods. Random.Range(int, int) and Random.Range(float, float). In your case, you use int version. For int version, second parameter is for maximum value exclusive, which means for 50% probability you should write Random.Range(1,3).

In float version (not your case), it second parameter is inclusive, which mean for 50% probability need to set Random.Range(0f,1f) > 0.5f.

Random.Range(0, 100) with a chance of 50 is exactly the same as Random.Range(0, 2).
Like in school, take everything you can outside the brackets.
You only want to use (0, 100) if your min chances are 1.