Final answer:
The size of an atom is difficult to measure because they are extremely small and cannot be seen with the na-ked eye. Scientists use methods like X-ray diffraction to calculate the size of atoms and molecules.
Step-by-step explanation:
The size of an atom is difficult to measure for several reasons. A crucial reason is that atoms are extremely small and cannot be seen with the na-ked human eye. The second reason is that our everyday experience and measuring techniques are not suitable for such small measurements.
To determine the size of an atom, scientists use various methods and instruments such as x-ray diffraction. This technique involves shining beams of X-rays through a crystal and measuring how much the beams are bent after passing through the crystal. By analyzing this data, scientists can calculate the size of the atom or molecule.