Question

where should we measure the volume of this graduated cylinder?
at the 21 ml marking
at the top of the meniscus
at the bottom of the meniscus
at the 22 ml marking

Explanation:

To measure the volume of a liquid in a graduated cylinder, we use the bottom of the meniscus (the curved surface of the liquid). This is the standard method in laboratory measurements for accuracy. The top of the meniscus is not used, and the markings (21 or 22 mL) are read based on the bottom of the meniscus. So the correct method is to measure at the bottom of the meniscus.

Answer:

at the bottom of the meniscus