Correct meaning of 'Blocking' in Randomized Block Design

Correct option is A

Blocking involves grouping participants who share a similar characteristic (a nuisance variable, e.g., age or gender) into blocks, then randomly assigning treatments within each block. This reduces unexplained variability and increases the precision of treatment comparisons.
Information Booster:
1. Blocking controls for known sources of variability that are not of primary interest.
2. Randomization still occurs — but only within each block.
3. Common blocking variables: gender, age group, pre-test scores.
4. RBD is especially useful when the sample is heterogeneous on a known variable.