If you wanted to prepare 500 mL of a 0.20M solution of dextrose (C6H12O6) in water, how much dextrose would you need?

18 g

Explanation:

The molar mass of dextrose is obtained as shown. Then the formula for number of moles is applied as shown in the image. Number of moles= mass/molar mass= concentration × volume. The volume is measured in dm3 hence the denominator of 1000. By making mass of solute the subject of the formula, we obtain the mass of dextrose requited to prepare the desired concentration of solution in the desired volume.

it can be observed without changing the identity of the object.

it depends on what substance you're talking about as well as many other factors. in quantum mechanics, the observation of particles affects the observers ability to measure certain properties. for example: you can know the velocity of a particle, but you can't know it's position; or you can know it's position, but not it's velocity. it's like trying to find out where a grain of sand is by throwing other grains of sand at it. once you find out where it is, it's been moved. it's also like trying to find an answer to the question of whether or not a tree falling in a forest makes a sound if nobody is there to hear it. paradoxically, the only way to find out is to be there and hear it.