Indicate whether each of the following is an exact number or a measured quantity subject to uncertainty. (a) the number of sheets of paper in a ream of paper (b) the volume of milk in a liter bottle (c) the distance between Earth and the sun (d) the distance between the centers of the two oxygen atoms in the oxygen molecule

Review each item to determine whether it's a perfect count or something that requires a tool to measure, hence subject to possible measurement error.

Analyze each case to determine if it's an exact quantity or a measured one. (a) The number of sheets of paper in a ream of paper is exact because a ream of paper is defined as 500 sheets - there should be no uncertainty there. (b) The volume of milk in a liter bottle is a measured quantity because it relies on the precision of physical measurement tools for liquids like a measuring cup or the bottle itself. (c) The distance between Earth and the Sun is a measured quantity due to factors like Earth's elliptical orbit creating variance in the measurement. (d) The distance between the centers of the two oxygen atoms in an Oxygen molecule is a measured quantity because it requires advanced tools to measure and is therefore subject to some degree of uncertainty.