Answer:
(B) The variance of an individual treatment average
Explanation:
ANOVA = Analysis of Variance
The correct answer is (B)
The mean square for error (MSE) in the analysis of variance (ANOVA) provides an estimate of the variance of an individual treatment average.
Unlike option C which refers to an individual observation, option B refers to a group of observations which are classified into a single treatment sample. The MSE measures (gives an estimate of) the variation within this treatment sample. In this case, the variation is in the average or the mean. This could be average texture, average strength, average penetration, etc.