The mathematical expression for mass percent is given by:

Put the values,

mass of zinc = 
=
or 65.4 g
Now, number of moles of zinc =
=
= 1.00 mole
Number of atoms of zinc is calculated by the Avogadro number.
Now, according to mole concept
molecules of enzyme consists of
atoms of zinc
So, 1 molecule of enzyme contains =
= 1 atom of zinc.
Hence, every carbonic anhydrase molecule consists of 1 atom of zinc.
The mass number is the total number of protons and neutrons in a nucleus of an element. The average atomic mass is the sum of the masses of an element's isotopes, each multiplied by their abundance.