When quartering a sample, retain two _________ quarters and reject the other two.

When quartering a sample, retaining two diagonally opposite quarters is essential for ensuring that the remaining sample is representative. This method aims to minimize bias and maintain homogeneity by evenly distributing the material taken for analysis. By selecting diagonally opposite quarters, you effectively balance the characteristics of the sample, allowing for a more accurate reflection of the whole.

If you were to retain either adjacent quarters or opposite quarters that are not diagonally arranged, you might end up with a sample that does not adequately represent the entire material, potentially introducing bias into your test results. The diagonal method balances and mixes different portions of the original sample, leading to more reliable and valid testing outcomes.