To purify a sample of crude benzoic acid, activated charcoal can be added to the hot solution to adsorb colored impurities before hot filtration and recrystallisation.

In an investigation, different masses of Charcoal A were added to 100 cm³ samples of hot crude benzoic acid solution. The experiment was repeated with Charcoal B.

The percentages of colored impurities removed are shown in the table below.

Table 1: Effectiveness of Charcoal A and Charcoal B

A student concluded:

"The most effective way to purify 100 cm³ of this benzoic acid solution is to add 1.5 g of Charcoal B."

Use the data in Table 1 to evaluate the student's conclusion.