Which statement best distinguishes organic from inorganic molecules?

• A. Organic compounds always contain carbon; most inorganic compounds do not contain carbon.
• B. Organic compounds never contain carbon.
• C. Inorganic compounds always contain carbon.
• D. All chemical compounds contain carbon.

Answer: (A)

The key idea here is that carbon is what distinguishes organic from many inorganic molecules. Organic compounds are structured around carbon backbones, often with hydrogen attached, giving them the chemistry we associate with living systems. In contrast, inorganic compounds are typically not built on carbon–hydrogen frameworks and many do not contain carbon at all.

This makes the statement that organic compounds generally contain carbon while most inorganic compounds do not contain carbon the best description. It captures the common rule used to differentiate these classes, even though there are a few carbon-containing inorganic substances (like CO2 or carbonates) and some organics with little hydrogen; those are exceptions rather than the rule.

Why the other ideas don’t fit: organic compounds aren’t limited to lacking carbon—they nearly always contain carbon; inorganic compounds aren’t required to have carbon—there are many carbon-containing inorganic substances; and not all chemical compounds include carbon.