Question #dae51

1 Answer
Apr 21, 2017

Answer:

#"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") :}#