Which of the following is a correct description of a double bond between two carbon atoms?

a double bond will produce four single bonds to form a tetrahedral shape.
a double bond between carbon atoms will eventually form a ring of carbons.
a double bond between carbon atoms is longer than a triple bond between carbon atoms.
a double bond will quickly reduce to single bonds to create three-dimensional tetrahedra.

Correct answer is: A double bond between carbon atoms is longer than a triple bond between carbon atoms.

Reason:
In a carbon-carbon double bonded system, each carbon has undergoes sp2 hybridization. Thus, it bond order of system is 2. While in case of carbon-carbon bonded system via triple bond, each carbon atom undergoes sp hybridization. The bond order in this case is 3. Further, extent of overlap in sp hybridized orbitals is more as compared to sp2 hybridized orbitals. Hence, a double bond between carbon atoms is longer than a triple bond between carbon atoms.