Why is the average atomic mass used when calculating grams of a substance? A. The number of isotopes in the sample is constantly changing. B. The average atomic mass is known to more significant figures, O C. The elements in the substance are mixtures of their isotopes. D. The exact weights of the isotopes are not known.​

B. The average atomic mass is known to more significant figures

answer is: naturally occurring solid, inorganic compound or element is mineral.

minerals usually have crystalline form, that means than crystal constituents (atoms, molecules or ions) are arranged in a highly ordered microscopic structure, forming a crystal lattice that extends in all directions.

for example magnetite is a mineral of iron oxide (fe₂o₃).

calcite is a carbonate mineral and the most stable polymorph of calcium carbonate (caco₃).

dolomite is an   carbonate mineral composed of calcium magnesium carbonate (camg(co₃)₂).