When metals are heated to high temperature, their __________ increases in general.

ANS:A - atomic vibration

Atomic vibration refers to the rapid movement of atoms within a material around their equilibrium positions. Atoms in a solid material are constantly in motion due to thermal energy, even at temperatures well below their melting points. This thermal energy causes the atoms to oscillate or vibrate around their average positions in the crystal lattice. The amplitude of atomic vibrations increases with temperature, meaning that atoms vibrate more vigorously at higher temperatures. This increase in atomic vibration leads to expansion of the material, as the atoms move further away from each other on average. It also affects the material's mechanical properties, such as its strength, ductility, and conductivity. In summary, atomic vibration is a fundamental aspect of the behavior of materials at the atomic scale, and it plays a crucial role in determining their properties and behavior, especially at elevated temperatures.