Final answer:
The volume measurement of 750 mL in a 1000-mL graduated cylinder with marks every 100 mL has three significant digits.
Step-by-step explanation:
When measuring the volume of a liquid in a graduated cylinder, like a 1000-mL graduated cylinder with marks every 100 mL, the recorded measurement should include all certain digits plus one estimated digit. Since this graduated cylinder allows for estimation to the nearest 100 mL, and 750 mL falls on a mark, we could reasonably assume that the measuring device permits us to estimate to the nearest 10 mL.
Therefore, the measurement of 750 mL has three significant digits: the '7' and the '5' are certain, and the last '0' is a placeholder that signifies precision to the hundredths place, assuming that the measurement was done with care.