chlorine has an average atomic mass of 35.45 amu. the two naturally occurring isotopes of chlorine are clorine-35 and chlorne - 37 why doesthis idicate that most clorine atoms contain 18 neutrons

See below.

Step-by-step explanation:

The two isotopes are Cl-35 and Cl-37.

The average atomic mass (35.45 u) is closer to 35 u, so most of the atoms are Cl-35.

mass number = number of protons + number of neutrons

A = p + n

35 = 17 + n

n = 35 - 17

n = 18

∴ Most chlorine atoms contain 18 neutrons.