Q.The compound that will react most readily with gaseous bromine has the formula (NEET)

Physical Properties and Addition Reactions of Alkenes

Physical properties parallel the alkanes: the first three alkenes are gases, the next fourteen are liquids, and higher alkenes are waxy solids; all are colourless and (ethene aside, which has a faint sweet smell) odourless; melting/boiling points rise along the series and fall with branching; solubility in water is low but good in organic solvents.

Addition reactions are the defining chemistry of the C=C double bond -- the strong sigma framework stays intact while the weaker pi bond breaks, letting two new sigma bonds form to the reagent's two parts:

• Hydrogenation (H2 / Ni, Pd or Pt) simply saturates the double bond to the alkane.
• Halogenation (Cl2 or Br2, no catalyst needed) adds rapidly to give a vicinal dihalide -- and bromine water's rapid decolourisation on contact with an alkene is the classic test for C=C/C-C-triple-bond unsaturation. Iodine adds far more slowly and reversibly (the diiodide tends to lose I2 again). …