A hydrocarbon in which two carbon atoms are joined by a double bond is called as an:

Correct answer: (b) Alkene

Explanation

Hydrocarbons are grouped by their carbon–carbon bonds:

• alkanes: single bonds only (C–C), such as ethane
• alkenes: at least one double bond (C=C), such as ethene
• alkynes: at least one triple bond (C≡C), such as ethyne

So a double bond makes it an alkene. An ionic bond is not a hydrocarbon at all.