Question

5. Which quantities must be conserved in all chemical reactions?

Answer 1

In a chemical reaction, the mass and energy must be conserved, as it states in the law of conservation of mass and also energy. Matter cannot be created not destroyed. 

Answer 2

A force of attraction that holds atom together 
When atoms react they form a chemical bond which is defined as a force of attraction that holds atom together. A force of attraction is defined as a kind of force that draws two or more objects together regardless of distance. There are two major categories of forces of attraction, one is intramolecular and intermolecular. Intramolecular forces is the presence of forces in atoms internally. While intermolecular is the force by which the force that is existent in two or more elements.