An electrically neutral atom has 17 electrons and 18 neutrons. what is it's atomic number?

Hello!

the atomic number is equal to the number of protons in the nucleus of an element's atom

because electrons are negative, neutrons are neutral, and protons are positive, you need the same number of protons as electrons to have an electrically neutral atom.

In this case, because there are 17 electrons, you need 17 protons to make the charge neutral

therefore, the atomic number is 17

this element is known as Chlorine

I hope this helps, and have a nice day!