What physical property do X-rays and light waves share?

X-rays and light waves both belong to the electromagnetic spectrum, which encompasses a range of electromagnetic radiation, and one key characteristic they share is that they can travel through a vacuum. This ability is due to their nature as transverse waves and the fact that they do not rely on a medium for propagation, differentiating them from mechanical waves such as sound. This property enables both X-rays and light to travel through the emptiness of space, which is crucial for applications such as astronomical observations and medical imaging.

In contrast, the other options incorrectly describe the nature of X-rays and light waves. They are not longitudinal waves; rather, they are transverse waves. They are also not forms of matter, as they are forms of energy. Additionally, they do not require a medium to propagate, which makes them unique compared to mechanical waves that need a material substance to transmit energy.