Final answer:
The mass of the unknown acid should be recorded to two decimal places to align with the least precise measurement involved in the calculation. Option b is correct.
Step-by-step explanation:
The mass of the unknown acid should be recorded to two decimal places. This is based on the rule that the recorded measurement should match the least certain measurement involved in the calculation, which is given as having three decimal places.
Therefore, the mass of the unknown acid should be reported to match that precision. In general, measurements should not have more significant figures than the least precise measurement when performing calculations such as sums and products.
For example, when determining pH levels, the significant figures in the concentrations dictate the number of decimal places, like in the case of a pH of 3.0 calculated from a concentration with a single significant figure leading to one decimal place in the result.
However, when a concentration has two significant figures, the pH should be reported with two decimal places.