5. In a sample of pure copper, all atoms have atomic numbers which are
(1) the same and the atoms have the same number of electrons
(2) the same but the atoms have a different number of electrons
(3) different but the atoms have the same number of electrons
(4) different and the atoms have a different number of electrons

(1) the same and the atoms have the same number of electrons

Explanation:

In a pure sample of copper, all the atoms have atomic numbers which are the same and the atoms have the same number of electrons.

Pure samples of a substance have a definite composition and are homogeneous all through.

To show this all the atoms that makes up the substance have the same number of electrons because they are of the same atom.

out of these options:

ability to burn paper

pure sodium reacting violently with water

the boiling point of water

helium does not tend to react with anything

i would say this is a physical property:

helium does not tend to react with anything

why? :

i said helium does not tend to react with anything because well, it reacts to ! but ability to burn paper, pure sodium reacting violently with water, & the boiling point of water are chemical or

physical properties: the properties of a substance that can be observed without changing the chemical makeup of the substance

chemical properties: properties of a substance relating to the chemical nature and reactivity of the substance

i think slash and