Quiet operation of a fan depends mostly upon the
a. motor balance.
b. balance of the blades.
c. weight of the blades.
d. material of the blades

B. balance of the blades.

Explanation:

If the all the blades of a fan do not have the same geometry and weight this leads to the imbalance of forces on the fan. Blade imbalance causes the improper spinning of the fan, this causes materials to rub against each other causing wear and tear and creating noise.

There are also other reasons why a fan might make noise but according to the options given here the balance of the blades is the best fit.

waves moving from a fast medium to a slow medium will experience a reflection as light travels more slowly than red light. total internal reflection occurs when the critical angle is.

b. a lightning bug, plug of grass, and a worm