Step 1: Compare the wavelengths in the options.
Visible light, ultraviolet and X-rays are all short wavelength, high energy radiation, while infra-red is longer wavelength, low energy thermal radiation.
Step 2: Think about how $\mathrm{CO_2}$ absorbs energy.
The Earth's surface, warmed by the sun, re-radiates energy back out mostly as long wave infra-red radiation, and the bending and stretching vibrations of the $\mathrm{CO_2}$ molecule happen to resonate at exactly these infra-red frequencies.
Step 3: Connect this to the greenhouse effect.
This resonant absorption is what traps outgoing heat near the Earth's surface, so the radiation strongly absorbed by $\mathrm{CO_2}$ near the ground is infra-red.
\[ \boxed{\text{Infra-red rays}} \]