Answer: C. 16. 8 g
Explanation:
when we are using significant numbers we have to keep in mind if the last digit is over 5 or down 5 to increase or decrease 1 digit the number to the left, if the last number is down 5, we decrease the number to the left 1 digit, but if the number is over 5, we can increase 1 digit to the number to left.
then we have this equation, as the 0 is not a significant number, we can omit this one.
9.78 g + 7.0 g = 16.78 g
as the last number is over 5 we can increase 1 digit to the number to the left, the we get the following result.
16.78 g = 16.8 g
because of that the correct answer is C. 16. 8 g