Question

A molecule of an unsaturated hydrocarbon must have(1) at least on single carbon-carbon bond

(2) at least one multiple carbon-carbon bond
(3) two or more single carbon-carbon bonds
(4) two or more multiple carbon-carbon bonds

Answer 1

An unsaturated hydrocarbon has a double or triple C-C bond as unsaturated literally means it is not saturated with atoms so there are "spare bonds" left.

Therefore:

A molecule of an unsaturated hydrocarbon must have 2 - at least one multiple Carbon-Carbon bond.

Answer 2

(2) at least one multiple carbon-carbon bond

Step-by-step explanation:

Hydrocarbons are organic compounds containing carbon (C) and hydrogen (H) atoms. Here, the skeletal structure is defined by the carbon-carbon bonds in which the C atoms can be linked to form linear chains or cyclic structures.

The C-C bonds in hydrocarbons are covalent in nature. The bonds can be single or multiple bonds. Structures in which the C atoms are linked by single bonds are called saturated hydrocarbons whereas multiple bonds between C atoms results in unsaturated hydrocarbons.

Therefore, a molecule of an unsaturated hydrocarbon must have at least one carbon-carbon multiple bond. The simplest example is ethene (C2H4) in which the C-C atoms are connected by a double bond.

Ethene → H2C=CH2