Question

which of these is true about pure substances?

A. they can only contain one type of atom

B. They can only contain one type of molecule

C. they may contain one type of atom or one type of molecule

D. they can contain different types of atoms and molecules​

Answer 1

Answer:

They can only contain one type of atoms, one type of molecules or one type of ionic salts

Explanation:

Remember that substances might be made of:

• just one type of atoms: the examples would usually be metals, such as sodium metal (Na) consisting of solely sodium atoms, iron (Fe) metal, gold (Au) metal, as well as gases (typically noble gases, He, Ne, Xe, Ar, Kr, Rn);
• molecules: the examples would be water consisting of $H_2O$ molecules, any gas, such as $O_2, F_2, SO_3, CO_2$ etc.;
• ions: the examples would involve any salt, such as NaCl, KBr, NaF etc.

That said, pure substances would only contain one type of atoms, one type of molecules or one type of ionic salts. Any additional components of different atoms, molecules or ionic salts would cause a pure substance to become a mixture of several substances.

Answer 2

Answer:

they may contain one type of atom or one type of molecule