Question

Name the hydrocarbon that is a liquid at STP
(A) Ethane
(B) Propane
(C) N-butane
(D) N-pentane

Answer 1

Hint: An organic chemical compound composed solely of hydrogen and carbon atoms is a hydrocarbon. Crude oil, natural gas, coal, and other essential energies are naturally built on hydrocarbons. Higher the number of carbons, higher in the intermolecular forces.

Complete step by step answer
Hydrocarbons are an important class of binary compounds. Only the elements carbon (C) and hydrogen consist of hydrocarbons (H). To form the structure of the compound, the carbon atoms bind together and the hydrogen atoms connect to them in several different configurations. Hydrocarbons are the principal components of oil and gas. They work in plastics, fibres, rubbers, solvents, explosives and industrial chemicals as well as raw materials as fuels and lubricants.
Thousands of potential hydrocarbon molecules are available. However, "alkanes" are the simplest kind. Alkanes have the $ {C_n}{H_{2n + 2}} $ formula, where n = 1,2,3 etc. For instance, we have $ C{H_4} $ for n=1, we have $ {C_2}{H_6} $ for n=2, etc.
Lower hydrocarbons with up to four carbon atoms are room temperature gasses, whereas higher hydrocarbons are liquid at room temperatures. Alkanes having C1 to C4 are in gaseous form and C5 to C17 are colourless, odourless and in liquid form, and from C18 onwards are colourless, odourless solids.
Ethane ( $ {C_2}{H_6} $ ) is in gaseous form at STP.
Propane ( $ {C_3}{H_8} $ ) is in gaseous form at STP.
N-butane is in gaseous form at STP.
N-pentane is found at room temperature in liquid form.
Hence, option D is the appropriate answer.

Note
In general, hydrocarbon molecules are arranged in a central structure, surrounded by hydrogen atoms, by one or more carbon atoms. Four major hydrocarbon groups exist: alkanes, alkenes, alkynes, and aromatic hydrocarbons.