Here's why:

* Organic compounds are defined as compounds containing carbon (C) and hydrogen (H) atoms, often with other elements like oxygen (O), nitrogen (N), etc.

* Inorganic compounds are all other compounds, including those that don't contain carbon or contain carbon bonded to elements other than hydrogen.

Calcium is a pure element, not a compound. It's a metal found on the periodic table. While it forms many compounds, such as calcium carbonate (CaCO3) found in bones and shells, calcium itself is inorganic.