Answer:
179.05 g/mol
Step-by-step explanation:
simple called the percentage of the molecular mass of each isotope and add them together. their sum is the mass of Halfnium.
thus
Hf --- 74/100 × 180 = 133.2
Hf --- 17/100 × 176 = 29.92
Hf --- 9/100 × 177 = 15.93
total mass = 133.2+29.92+15.93
= 179.05 g/mol