Final answer:
To round 16.8477 L to three significant figures, the number becomes 16.8 L since the fourth digit (4) is less than 5, which means we do not increase the third digit (8).
Step-by-step explanation:
To round 16.8477 L to three significant figures, we start by looking at the first three non-zero digits, which are 1, 6, and 8. The fourth digit after the decimal point is 4, which is less than 5, so we do not need to round up the third significant figure. Thus, 16.8477 L rounded to three significant figures is 16.8 L.