How is the phenomenon of refraction useful to humanity

Yes, it does have an important role in humanity!

Explanation:

In human life, refraction of light plays an important role. It has many applications in optics and imaging technology. Some of the applications are: Refraction concave and convex glasses are used to correct the refractive errors of human eyes.

the density(ratio between mass and volume as m/v) decreases from top to bottom in periodic table group as the size increases and nuclear charge decreases. but in periods density increases from left to right as atom size decreases and nuclear charge increases.

"record the time to complete a chemical reaction" would most likely be part of a lab procedure.