Final answer:
Options A (79,34X) and B (79,35X) represent isotopes as they have the same atomic number but different mass numbers, indicating different numbers of neutrons.
Step-by-step explanation:
To identify which of the following represent isotopes, we should compare their atomic numbers (the lower number) and their mass numbers (the higher number).
- A: 79,34X
- B: 79,35X
- C: 78,34X
- D: 81,36X
Isotopes are atoms with the same number of protons but different numbers of neutrons. Thus, the atomic numbers should be the same for isotopes. Looking at the given options, A (79,34X) and B (79,35X) have the same atomic number (34), indicating they represent isotopes of the same element with different numbers of neutrons.
Option C (78,34X) is not an isotope of A and B because its atomic number is different. Similarly, Option D (81,36X) has a different atomic number, so it is also not an isotope of A and B.