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.