The combination of two or more atoms, from the same or different elements, creates a(
a. element
c. molecule
b. atom
d. mixture

By definition, we have to:

The molecule is formed by two or more atoms and presents all the physical and chemical properties of a substance.

We have two possible cases:

1) The atoms that form the molecules can be the same: For example, we have oxygen. The oxygen molecule has two oxygen atoms.

2) The atoms that form the molecules are different: For example, the water molecule (H2O). This molecule has 2 hydrogen atoms and an oxygen atom.

The combination of two or more atoms, from the same or different elements, creates a molecule.

a compound is a molecule made of atoms from different elements.

a. by the combination of an unlimited number of elements

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).