Right option is (c) Concentration error
The best I can explain: There are a number of errors that may occur in the electronic cell counting technique. Briefly, these errors are categorized as follows:
Aperture Clogging, Uncertainty of Discriminator Threshold, Coincidence Error, Settling Error, Statistical Error, Error in Sample Volume, Error due to Temperature Variation, Biological Factors, Dilution Errors, Error due to External Disturbances.