# Question cd5d6

Oct 20, 2017

$54$

#### Explanation:

The trick here is that it doesn't matter which isotope of xenon you're dealing with, as long as it is a neutral atom, the number of electrons that surround the nucleus will always be equal to the number of protons located inside the nucleus.

In your case, an atom of xenon-135 contains $54$ protons inside its nucleus, as described by the element's atomic number.

""_(color(white)(1)54)^135"Xe " implies " " {("protons + neutrons" = 135 -> "the mass number"), (color(white)("neutrons + ")"protons" = 54 -> "the atomic number") :}#

As you know, any neutral atom, regardless of its mass number, will have

$\text{no of protons " = " no. of electrons}$

This implies that a neutral atom of xenon-135 will have $54$ electrons surrounding its nucleus.