Solution exposure to air and light with the manual processing technique can be avoided by using a:

a. thermometer
b. tank cover
c. timer
d. stirring rod

Answer is B. Tank cover.

Explanation:

A tank can be described as a container,usually large, but sometimes small, which is used to house gases and liquids.

A cover , which can also be referred to as a lid, serves a  role as a closure or seal.

The use of a tank cover will prevent the solution from being exposed to air or light.

there’s no image attached but i can if you want: )

did you fail the test? xd