Question

Question #dae51

Answer 1

`"120 neutrons"`

Explanation:

The thing to remember about an atom's mass number, `A`, is that it gives you the number of protons and neutrons present inside said atom's nucleus.

`color(blue)(ul(color(black)("mass number = no. of protons + no. of neutrons")))`

For any atom, the atomic number, `Z`, gives you the number of protons located inside the nucleus. You can thus say that

`color(blue)(ul(color(black)("mass number = atomic number + no. of neutrons")))`

Using `A` and `Z`, you can say that

`color(blue)(ul(color(black)(A = Z + "no. of neutrons")))`

This means that the number of neutrons will be equal to

`"no. of neutrons" = A - Z`

In your case, this isotope of element `"X"` has

`"no. of neutrons" = 168 - 48 = 120`

neutrons located inside its nucleus. In isotope notation, you can write this isotope as

`""_(color(white)(1)color(green)(48))^color(blue)(168)"X" -> {( color(green)(48)color(white)(.)"protons"), (color(blue)(168)color(white)(.)"protons and neutrons"), (168 - 48 = "120 neutrons") :}`