Natural selection can be best defined as the

The question is inappropriate which should be as the following:

A.) What is the dilution factor after Step 1? (2 points)

B.) What is the final/total dilution factor at the end of Step 2 from the starting stock?

1. Df- 1/4 r 4 fold or 4 times

2. Final dilution factor- 12 times

Explanation:

A serial dilution refers to the reduction in the concentration of the solute in a solution in which the solution is diluted with the same dilution factor.

In the given question,  

The dilution factor will be calculated as the following:

The amount of concentrated solution divided by the total volume of solution

The volume of water added- 300 ul

1. The total volume of solution will be- 100+ 300 ul= 400 ul

Df= 100/400

= 1/4 r 4 fold or 4 times

2.The volume of solution added- 100 ul  

solution added to- 200ul  

The total volume will be- 300  ul  

Df- 100/300 or 3 times

Therefore the final dilution factor will be- 4 x 3= 12