Question

which statement is true about all the atoms of a given element?
a they are the same size as the atoms of all other elements.
b they can have a different number of protons.
c they all have the same number of protons.
d they have the same number of neutrons.

Explanation:

The definition of an element is that all atoms of a given element have the same number of protons (atomic number). Atoms of different elements have different sizes (so option a is wrong). If atoms of the same element had different numbers of protons, they would be different elements (so option b is wrong). Atoms of the same element can have different numbers of neutrons (isotopes, so option d is wrong).

Answer:

C. They all have the same number of protons.