An isotope of an element, atomic number z, has a mass number 2z+4. how many neutrons are there in the nucleus of the element?
*multiple choice*
a) z+4
b) z+2
c) z
d) 4

A) Z+4

Explanation:

Atomic number of the isotope = Z

Mass number of the isotope = 2Z+4.

Atomic number = Number of protons in the atom = Number of electrons in the atom

Mass number = Number of protons in the atom + Number of neutrons in the atom

Hence number of neutrons = Mass number - Number of protons

= 2Z + 4 - Z = Z + 4

Hence the required answer to the question is represented by option A which is Z + 4.