Answer:
<em>The branch of natural science that deals with the composition and constitution of substances and the changes that they undergo as a consequence of alternations in the constitution of their molecules is chemistry.</em>
Explanation:
Answer is periodic because only happens in certain times
The answer should be <span>balance electrically
</span><span>Chemical reactions that form ions should have a balanced charge. The example of the reaction is HCl. When forming ions, the equation should be:
HCl => </span>

+

In this case, the hydrogen has one plus charge and chlorine has one negative charge. The resultant should be zero, so it's balanced.
Six elemental gases are composed of such exceptionally stable atoms that they almost never react with other elements. They are the gases that make up Group 0 (the rightmost column) of the periodic table: helium (He), neon (Ne), argon (Ar), krypton (Kr), xenon (Xe), and radon (Rn).
Transverse waves can be produced on a rope by moving one end of the rope up and down.The movement causes motion in the particles that make up the rope and the rope itself becomes the medium. The particles move perpendicular to the propagation. The movement also causes crests(highest point of the wave) and troughs (lowest point of the wave) which move along the direction of propagation.