In the question below is given a statement followed by two options numbered 1 and 2. Based on this choose the correct option. Statement: Serial dilutions are routinely used in microbiology to estimate the number of microorganisms in samples with an unknown concentration. Option 1: By diluting one ml of a sample containing one billion bacterial cells/ml in nine ml of diluent, you will get a concentration of one hundred million bacterial cells/ml. Option 2: Serial dilutions are done until you get a more easily countable concentration of 30 to 300 bacterial cells/ml. Options:

Correct option is C

Serial dilution is a common microbiological method used to reduce a dense culture of cells to a more usable concentration, typically to allow for accurate colony counting on agar plates.
Option 1 is correct: If you dilute 1 ml of a sample with 1 × 10⁹ CFU/ml (colony forming units) into 9 ml of sterile diluent (such as sterile water or buffer), the total volume becomes 10 ml. The dilution factor is 1:10, which means the concentration becomes:

i.e., 100 million bacterial cells/ml — so the statement is correct.
Option 2 is correct: In microbial enumeration (especially using the pour plate or spread plate technique), plates yielding 30 to 300 colonies are considered statistically reliable for accurate colony counting. Too few colonies (<30) may not be representative, and too many (>300) may cause overlap and counting errors.
Therefore, both statements are scientifically accurate, and the correct answer is Option (c).