Final answer:
The correct answer is A) 109.3 g, following the rule for addition that dictates the result has the same number of decimal places as the value with the fewest decimal places, which in this case is 2.51 g with two decimal places.
Step-by-step explanation:
The student asks for the sum in the correct number of significant figures for the expression: 4.392 g + 102.40 g + 2.51 g. The rule for addition and subtraction with significant figures dictates that the result should be rounded off to the same number of decimal places as the number with the fewest decimal places. In this case, the number with the fewest decimal places is 2.51 g, which has two decimal places. Therefore, when performing the addition, the sum is calculated to be 109.302 g on a calculator, but must be reported as 109.30 g to adhere to the significant figures rule. The correct answer is A) 109.3 g.