16 is the right answer if you use PEMDAS only: (8 ÷ 2) × (2 + 2)

You added brackets and changed the answer. 2(2+2) is a single term, and if you break it up then you change the answer (because now the (2+2) is in the numerator instead of in the denominator).

1 is the right answer

The only right answer

both are correct answers

Nope, 1 is the only correct answer.

this is also one of the reasons why postfix and prefix notations have an advantage over infix notation

Except they don't. This isn't a notation problem, it's a people don't remember the rules of Maths problem.