Which two notation represent atoms that are isotopes of the same element

When an isotope forms, there is 2 things that stay the same in the element.
Those are the electrons and the protons. 
The only thing that is changed is neutrons. 
That is because the atomic mass is changed, and the atomic mass is the protons plus the electrons. 

Ci hope  it  you

It is a mixture. simply put, a compound must be pure, that is, of only one chemical structure and composition. a mixture is made of different chemical substances (i.e. elements, molecules, compounds) that are not chemically bonded to each other, but instead physically grouped together, as in the case of gasoline (a homogeneous solution).