Carbon dioxide is found in the free state as well as in the combined state.

The atmosphere of the earth contains 0.03% of carbon dioxide by volume in the free state.

In the combined state, it occurs in carbonates such as limestone (\(\rm CaCO_{3}\)),                       magnesite (\(\rm MgCO_{3} \)), carbohydrate (\(\rm C_{6}H_{12}O_{6} \)), proteins, fat, etc.