Ethene hi jayga answer . bcz ethane inme se sabse jyada unstable h to iski heat of hydrogenation sabse jyada hogy. Ok bro got it

**Maximum Heat of Hydrogenation in Alkenes**

The heat of hydrogenation is a measure of the stability of an alkene. It represents the amount of energy released when one mole of an alkene reacts with excess hydrogen to form one mole of the corresponding alkane. The higher the heat of hydrogenation, the less stable the alkene and the more reactive it is.

Let's analyze the four given alkenes and determine which one has the maximum heat of hydrogenation.

**1. 1-Butene:**
1-Butene is a terminal alkene, meaning it has a double bond at the end of its carbon chain. Terminal alkenes are generally less stable than internal alkenes due to the presence of a methyl group at one end, which can cause steric hindrance. Therefore, 1-butene is less stable and has a higher heat of hydrogenation compared to internal alkenes.

**2. cis-2-Butene:**
Cis-2-butene is an internal alkene with a double bond between the second and third carbon atoms. It does not possess any methyl groups at the ends, resulting in less steric hindrance compared to 1-butene. Therefore, cis-2-butene is more stable and has a lower heat of hydrogenation than 1-butene.

**3. trans-2-Butene:**
Trans-2-butene is also an internal alkene with a double bond between the second and third carbon atoms. It has the same carbon skeleton as cis-2-butene but differs in the arrangement of substituents around the double bond. Trans-2-butene is more stable than cis-2-butene due to the absence of cis-interactions between the substituents. Therefore, trans-2-butene has a lower heat of hydrogenation than cis-2-butene.

**4. Ethene:**
Ethene is the simplest alkene with a double bond between two carbon atoms. It does not possess any substituents or methyl groups, resulting in the highest degree of stability among the given alkenes. Ethene has the lowest heat of hydrogenation compared to the other alkenes.

**Conclusion:**
Among the given alkenes, ethene has the maximum heat of hydrogenation. This is due to its simple structure without any substituents or methyl groups, making it the most stable alkene.