A mallet weighing ________ must be used to tap the sides of the bowl after rodding each layer.

The correct answer states that a mallet weighing 1.25 +/- 0.5 lbs is the appropriate choice for tapping the sides of the bowl after rodding each layer. This specific weight provides a balance that is sufficient to ensure proper compaction of materials while avoiding any risk of damaging the bowl or the sample being prepared.

Using a mallet that is too light might not adequately compact the material, leading to incomplete consolidation and potential flaws in the final testing results. On the other hand, a mallet that is too heavy could cause excessive force, potentially risking injury or damage to the testing apparatus. The specified weight range allows the user to effectively achieve the necessary compaction without compromising accuracy or safety.

Ultimately, this choice reflects the recommended practice in standard testing methods, ensuring that practitioners utilize the right tools to obtain reliable data and consistent results.