Question

Compare an electrically neutral atom of oxygen and an isotope of oxygen. in own words

Answer 1

neutral implies that the amount of electrons  = amount of protons

so for oxygen, protons = 8

isotopes have equal number of protons but differ in number of neutrons , so that affect the mass since  :
protons + neutrons = atomic mass

Hope this helps 

Answer 2

Explanation:

An isotope is defined as the specie which contains same number of protons but different number of neutrons.  

For example, $^{16}_{8}O$ and $^{17}_{8}O$ are isotopes.

In a neutral oxygen atom, there are 8 protons and 8 neutrons.  

As it is known that in a neutral atom the number of protons is equal to the number of electrons.  

This means that in a neutral oxygen atom there are also 8 electrons.

Whereas in $^{17}_{8}O$ is an isotope of oxygen atom whose atomic number is 8 and atomic mass is 17.

In $^{17}_{8}O$, there are 8 protons and 9 neutrons.