The type of bond that forms a fatty acid to a 3-carbon backbone (specifically, glycerol) is an ester bond.

Here's why:

* Glycerol: This is a 3-carbon molecule with three hydroxyl (-OH) groups.

* Fatty Acid: These are long hydrocarbon chains with a carboxyl (-COOH) group at one end.

Ester Bond Formation:

1. The carboxyl group of the fatty acid reacts with one of the hydroxyl groups of glycerol.

2. Water (H2O) is removed, and the remaining oxygen atom forms a bond between the carbon of the carboxyl group and the carbon of the hydroxyl group.

3. This bond is called an ester bond.

Result:

This process creates a triglyceride, which is a molecule composed of three fatty acids attached to a glycerol backbone. This is the primary form of fat storage in the body.