I do not agree with the statement.
The "substance" can be a compound.  It's "pure" 
as long as there's nothing else in it but its name.
'Pure' water is 100% H₂O with nothing else in it.
'Pure' table salt is 100% NaCl with nothing else in it.
'Pure' carbon dioxide is 100% CO₂ with nothing else in it.
These example substances are all compounds, not elements.
 
        
             
        
        
        
Answer:

Explanation:

1+7 = 6+2 =8 -protons
1+15 = 12+4 = 16 -  protons +neutrons
 
        
             
        
        
        
As the rollercoaster goes up. kinetic energy changes to gravitational potential energy. When it moves back down, gpe changes back to ke.
        
             
        
        
        
Answer:
zero
Explanation:
For a solid conducting sphere, charges are present on the surface of the sphere due to a phenomenon known as electrostatic sheilding. This affects the charge present in the body and makes it zero. However, the electrostatic potential appears to be equal to the whole present point that shows on the surface. The surface of a spherical conducting solid sphere is known as an equipotential surface. Thus, the potential difference between the two opposite points on the surface of the sphere will also be zero.