Answer :
The atomic mass of hafnium is 178.55g
The average atomic mass of the atom is defined as the average of the atomic mass of the atom with respect to their percentage.
average atomic mass = Sum of atomic weights
100
In hafnium out of 100 atom, the number of atoms with mass of 176 is 5, the number of atoms with a mass of 177 is 19, the number of atoms with mass 178 is 27, the number of atoms with mass 179 is 14 and the number of atoms with mass 180 is 35. Therefore the average atomic mass of hafnium is,
= (176×5) + (177×19) + (178×27) + (179×14) + (180×35)
100
= 17855 = 178.55g
100
Hence the atomic mass of hafnium is 178.55g
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