How would you determine the amount of matter in a substance?

The measurement of any quantity is a crucial part of laboratory procedures and even daily life since it gives clear insight into the amount of a drug and enables it to be eaten appropriately.

Any material's quantity may be calculated with the use of a suitable scale, which varies depending on the condition of the substance.
For example, using the millilitre or litre scales, one can estimate the volume of a liquid material. So, when we refer to five litres of water, we are aware of its weight. Similar calculations might be made for solids using grammes or kilogrammes, and we are familiar with the weight of one gramme. These are the fundamental scales for calculating the quantity of any material.

Fundamental quantities are those particular quantities, on the other hand, that are unique in nature and cannot be represented in terms of any other quantities. In addition to being a fundamental quantity, the amount of a material may also be stated in terms of moles. The Avogadro's number is the number of particles that make up one mole of any material.

Hence, the correct option is (A).