An isotope of xenon has an atomic number of 54 and contains 77 neutrons. What is the xenon isotope's mass number? 23 54 77 131

Lets get this organized:-

Atomic number ⇔ Protons

54 ⇔ 54 protons

Atomic mass ⇒ Protons + Neutrons

? ⇒ 54 + 77

54 + 77 = 131

The atomic mass would equal →→→ 131

So, our final answer would be 131