Question

Alkenes and alkynes are:
A.Saturated aliphatic hydrocarbons
B.Unsaturated aliphatic hydrocarbons
C.Unsaturated hydrocarbons
D.Cyclic hydrocarbons

Answer 1

Hint: For this question we must have the knowledge about the terms related to hydrocarbons. They contain a double and a triple bond respectively. Ethene and ethyne are examples of alkenes and alkynes.

Complete step by step answer:
Mainly hydrocarbons are classified into two classes. Aromatic hydrocarbons are those which have pi conjugated systems, are cyclic, follow Huckel rule and aliphatic hydrocarbons are cyclic or acyclic hydrocarbons but without any pi conjugation.
Further aliphatic hydrocarbons are classified into two parts, saturated hydrocarbons and unsaturated hydrocarbons. Both alkenes and alkynes are the class of aliphatic hydrocarbons.
Saturated hydrocarbons:
Alkane is those hydrogen and carbon containing compounds which have only single bonds. They are the part of saturated hydrocarbons. Some examples of Alkane are methane, ethane, propane, butane etc.
Unsaturated hydrocarbon:
They are those compounds which contain double or triple bonds. They are further classified as alkenes and alkynes. Alkenes are those unsaturated hydrocarbons which contain double bonds and alkynes are those hydrocarbons which contain triple bonds.
It is not necessary that all bonds should be double or triple bonds. The presence of at least one triple or double bond makes the compound unsaturated. However to be saturated hydrocarbon, all the bonds should be single bonds and no double and triple bonds must be present.

Hence the correct option is B.

Note:
Generally aliphatic hydrocarbons are flammable; hence they are widely used as fuel, Such as Methane and LPG. Methane is used in Bunsen burners and acetylene is used in welding.