What kind of force exists when all the forces cancel each other out (net force= 0n)?
a. non-contact
b. contact
c. balanced
d. un-balanced

Balanced force exists when all forces cancel each other out. Un-balanced force would be a man shoving another man. Non contact force is a force that doesn't touch you, like weight. Contact force would be like a elephant standing on-top of a ball. Therefore C. is the answer.

The answer is joseph is observing the colour of the reaction mixture to see whether proteins are present in the given solution.