Which of these is the definition of the EXPLODE Physical Hazard? A) Chemicals that are likely to be flammable and/or support a fire
B) Chemicals that release high pressure and could cause bodily injury
C) This is a potential reaction that could take place when two chemicals are
mixed together.
D) This is when a chemical breaks down and could become harmful when
handled improperly or exposed to extreme temperatures

Explanation:

Physical hazard means a chemical for which there is scientifically valid evidence that it is a combustible liquid, a compressed gas, explosive, flammable, an organic peroxide, an oxidizer, pyrophoric, unstable (reactive) or water-reactive.

EXPLODE:  

to expand with force and noise because of rapid chemical change or decomposition, as gunpowder or nitroglycerine (opposed to implode).

to burst, fly into pieces, or break up violently with a loud report, as a boiler from excessive pressure of steam.

answer : a model is often used to explain and make things easier to understand when any scientific topic needs to be demonstrated and explained.

as in this case where a scientist wants to use a model to present the results of his detailed scientific investigation. he should do it as it will him to make the audience understand the concept in a much better way. also, it can be changed according to new scientific understandings.