Answer :
An atomic mass unit is defined as 1/12 th of the mass of carbon-12 atom.
The mass of an atom is mainly due to its protons and neutrons in the nucleus.
Weight of a proton is 1.6 x 10^-27 kg
Weight of a neutron is 1.6 x 10^-27kg
However weight of an electron is 9 x 10^-31kg and hence is negligible in calculation of amu
A chlorine atom has 17 protons in its nucleus and 18 neutrons in its nucleus
Its atomic number is 17
Amu weight of Cl= weight of protons+ weight of neutrons
=17+18
=35amu
Hence the average atomic mass unit of chlorine atoms will be 35 amu
Disclaimer:
The value is taken for easier calculation and is not accurate upto 3 decimals
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