Is this an isomormorphism: R/I -> R defined by r + I -> r

Problem: This is not necessarily well-defined.

For instance, let R = Z and I = 2Z.
Then, this map states that 0 + 2Z → 2.

However, 0 + 2Z = 2 + 2Z, and 2 + 2z → 2, and 0 ≠ 2.

I hope this helps!