Which of the following hydrocarbons is classified as unsaturated?

• A. $C_4{H}_{10}$ (butane)
• B. $C_6{H}_{14}$ (hexane)
• C. $C_3{H}_8$ (propane)
• D. $C_2{H}_4$ (ethylene)

Answer: (D)

Verified step by step guidance

1. Understand the definition of saturated and unsaturated hydrocarbons: Saturated hydrocarbons contain only single bonds between carbon atoms, while unsaturated hydrocarbons contain one or more double or triple bonds.
2. Examine the molecular formulas given and compare them to the general formulas for alkanes (saturated) and alkenes/alkynes (unsaturated). The general formula for alkanes is \(C_nH_{2n+2}\), for alkenes is \(C_nH_{2n}\), and for alkynes is \(C_nH_{2n-2}\).
3. Check each hydrocarbon: For butane (\(C_4H_{10}\)), hexane (\(C_6H_{14}\)), and propane (\(C_3H_8\)), verify if their hydrogen count matches the alkane formula \(C_nH_{2n+2}\), indicating saturation.
4. For ethylene (\(C_2H_4\)), compare its formula to the alkene formula \(C_nH_{2n}\). Since it fits this formula, it suggests the presence of a double bond, classifying it as unsaturated.
5. Conclude that ethylene is the unsaturated hydrocarbon among the options because it contains a double bond, unlike the others which are saturated alkanes.