The agar plate with the most countable colonies should be determined by using a colony forming unit (CFU) calculator.
A colony can be defined as a group of visible mass of microorganisms such as bacteria, fungi, that originated (cultured) from a single-mother cell and are grown on a solid agar medium.
In order to determine the most countable colonies, we have to count the total number of colonies by using a hemacytometer and then use a colony forming unit (CFU) calculator to determine the cfu/mL.
Note: You should choose a dilution factor based on the total number of colonies contained in the agar plate.
Finally, input the correct dilution factor into the colony forming unit (CFU) calculator to determine which agar plate has the most countable colonies.
Read more on dilution factor here: https://brainly.com/question/24881505