What can be concluded about the atom from knowing that oxygen-18 has an atomic number of 8?

I use this method to remember:
Let's use A as the mass number, and A = protons + neutrons 
Z is the atomic number, which is protons
To get neutrons, you subtract A from Z.
So in this sense, neutrons = 18 - 8 = 10 
I hope this helps with your work. :)

4- c, because all matter stays the same no matter what. it is still there. 5- b, because matter is known as mass. 6-c because, flammability is a chemical property. malleability is changing the shape of an object.

Butterfly wingspan is 7.7