Question

How many of the following five alkenes: propene, butene, pentene, hexene and heptene are liquid at room temperature?
a.$1$
b.$2$
c.$3$
d.$4$

Answer 1

Hint: Alkene consists of a carbon-carbon double bond. This double bond makes alkene different from alkane in terms of its physicals as well as chemical properties. At room temperature, alkenes are found in all three phases i.e. solid, liquids or gases.

Complete answer:
Alkenes are a family of hydrocarbons found in crude oil. There is a minimum of one carbon-carbon double bond. This makes a great difference in the chemistry of compounds of the family. Like alkanes, alkenes burn in air and form carbon dioxide and water. Their melting and boiling points are similar to that of alkanes but isomers of cis alkenes have lower melting points than of trans isomers. Alkenes have weak dipole-dipole interactions due to the electron attracting $s{p^2}$ carbon.
For lower alkene like ethene, propene or butene are gases, mid-range carbon atoms like pentene, hexene, heptene etc. are liquid while higher ones above $C17$ are solid form at room temperature. This is because the intermolecular forces acting on the carbons of alkenes get stronger with the increase in the size of the molecules.
Thus, in this question; out of five, only three are liquids while the other is gases.

Option c is the correct answer.

Additional information:
Alkenes have double compounds which are colourless and odourless in nature. However, ethene is colourless gas but has a sweet odour. Alkenes are insoluble in water as they have nonpolar characteristics but are soluble in a nonpolar solvent like ligroin, benzene etc.

Note:
Alkenes, particularly ethene are very much important in the chemical industry. Alkenes are also used in the chemical industry for the manufacture of plastics and are used as fuels. In the presence of oxygen, ethene reacts explosively thus is not good as a fuel.