Which of the following halogens is employed for the test of unsaturation?

Options

A. Iodine
B. Bromine
C. Chlorine
D. Fluorine

Answer

B

Explanation

The formation of addition compounds with `Br_(2)` serves as a test for the presence of carbon-carbon multiple bonds. If we add bromine to an alkene (or alkyne), the red brown color of the bromine solution disappears almost instantly as long as the alkene (or alkyene) is present in excess. This behaviour contracts markedly with that of alkanes which do not react appreciably with `Br_(2)` or `Cl_(2)` at room temperature and in the absence of light.
Although `I_(2)` solution is also colored, it is not used because reaction with `I_(2)` is quite slow.