Chemistry Regents Practice Test

A sample of matter can be identified as copper if what characteristic is observed?

1. The sample is magnetic

2. Each atom has 29 protons

3. It conducts electricity

4. It is a solid at room temperature

The correct answer is: Each atom has 29 protons

A sample of matter can be identified as copper if each atom has 29 protons because the number of protons in an atom defines its identity as an element. Copper is element number 29 on the periodic table, meaning that every atom of copper has exactly 29 protons in its nucleus. This characteristic directly ties to the uniqueness of copper as an element. Other characteristics, while they may be associated with copper, do not definitively identify it. For instance, while it is true that copper conducts electricity and is a solid at room temperature, those traits can also apply to other materials. Additionally, copper is not magnetic, which further emphasizes that the definitive characteristic for identifying copper is its atomic number, conveyed through the count of protons.