Which of the following causes excitation in atoms?

The process of excitation in atoms occurs when an atom absorbs energy that allows one of its electrons to move from a lower energy level to a higher energy level. Among the options provided, heat or light photons are the primary drivers of this excitation. Photons, which are packets of light energy, can carry sufficient energy to promote an electron to a higher energy state upon absorption.

When an atom encounters photons with the right energy (specific to the differences between the energy levels of the electrons in that atom), the electrons can absorb that energy and move to an excited state. This concept is fundamental in various phenomena, such as the emission of light in fluorescent materials or the operation of lasers, where specific photon energies are used to achieve electron excitation.

In contrast, low energy collisions might not provide enough energy to cause excitation; sound waves typically do not carry the necessary energy at an atomic scale to affect electron states; and the absence of energetic particles means there's no external energy source available to facilitate the process of excitation. Therefore, the option referring to heat or light photons correctly identifies the means by which excitation occurs in atoms.