When bromine is added to ethene at room temperature, the compound formed is

Step 1: Analyze the question We are asked for the product when bromine (Br₂) reacts with ethene (C₂H₄) at room temperature.

Step 2: Explain the concept Ethene is an alkene, so it has a C=C double bond. Alkenes are unsaturated and undergo addition reactions. In the reaction with bromine, the double bond breaks and one bromine atom attaches to each carbon of the former double bond. This is also the classic test for unsaturation: the reddish-brown bromine water or bromine in tetrachloromethane is decolorised.

Step 3: Solution

CH₂=CH₂ + Br₂ → CH₂Br–CH₂Br

• Each carbon originally in the double bond picks up one Br atom.
• The product has the two Br atoms on different carbons (positions 1 and 2).
• The C=C double bond becomes a C–C single bond, so the product is saturated, which makes it an ethane derivative, not an ethene.

Step 4: Eliminate the wrong options

• A. 1,1-dibromoethane: Both Br atoms would be on the same carbon, which is not what happens in addition across a double bond.
• B. 1,2-dibromoethene: The name ends in "ene", so it would still have a double bond. Addition removes the double bond.
• C. 1,1-dibromoethene: It has the wrong position and still has a double bond.
• D. 1,2-dibromoethane: Correct. The Br atoms are on different carbons and the product is saturated.

Answer: D. 1,2-dibromoethane

Tip: Remember "alkenes add, alkanes substitute." If a reaction involves an alkene and a halogen, the product name will end in -ane, with the halogens on the two carbons that held the double bond (1,2-). Also, a quick sign of this reaction in the lab is the bromine color disappearing.