Question

The composition of the nuclei of three atomic species X, Y, and Z are given as follows.

	X	Y	Z
Number of protons	18	17	17
Number of neutrons	19	18	20

Explain the relation between the following:

Y and Z

Answer 1

Atomic species Y and Z are isotopes because they have the same number of protons (17) but different numbers of neutrons (18 and 20).

Their atomic number is 17, but their mass numbers are different:

• Y = 17 + 18 = 35
• Z = 17 + 20 = 37

Hence, Y and Z are isotopes of the same element, chlorine.