Do all isotopes of an element have the same atomic number?

What are the percent by mass of copper in penny lab

Astudent reacts 13 moles of iron with 21 moles of oxygen according to the following equation:

Which of the following describes a compound? (hint: carbon and oxygen bo a. a piece of pure carbon, containing only carbon atoms b. oxygen gas surrounding a solid piece of carbon c. a substance made of two oxygen atoms for each carbon atom carbon and oxygen atoms mixed without being bonded together