Which of the following is NOT an unsaturated carbon compound?

The correct answer is option 3. Butane.

The compound Butane \((C_4H_{10})\) is not an unsaturated carbon compound; it is a saturated hydrocarbon.

Butane consists of only single bonds between carbon atoms, which means it is fully saturated with hydrogen atoms. Unsaturated carbon compounds contain at least one carbon-carbon double or triple bond, which results in fewer hydrogen atoms bonded to the carbon atoms.

So, the correct option is: 3. Butane