Unsaturated hydrocarbons ethyne,.

Explain
Because Unsaturated hydrocarbons like ethyne, also known as acetylene, burn to produce a yellow, sooty flame due to incomplete combustion in air. The flame is sooty because the percentage of carbon is comparatively higher than that of alkanes and so does not get completely oxidized in air.

Identification of the Hydrocarbon Z

To identify the hydrocarbon Z that burns with a yellow sooty flame, we need to consider the characteristics of different hydrocarbons and their combustion processes. The hydrocarbons under consideration are A) Butane, B) Propane, C) Ethane, and D) Ethene.

1. Butane (C4H10)
Butane is a hydrocarbon with four carbon atoms and ten hydrogen atoms. It is commonly used as a fuel for heating and cooking purposes. However, when burned, butane produces a blue flame with minimal soot. Therefore, it can be eliminated as the hydrocarbon Z.

2. Propane (C3H8)
Propane is a hydrocarbon with three carbon atoms and eight hydrogen atoms. It is also commonly used as a fuel for heating and cooking. Like butane, when propane is burned, it produces a blue flame with minimal soot. Hence, propane can be eliminated as the hydrocarbon Z.

3. Ethane (C2H6)
Ethane is a hydrocarbon with two carbon atoms and six hydrogen atoms. It is primarily used as a fuel and a raw material for the production of chemicals. When ethane is burned, it produces a blue flame similar to butane and propane, indicating complete combustion and minimal soot. Therefore, ethane can be eliminated as the hydrocarbon Z.

4. Ethene (C2H4)
Ethene is a hydrocarbon with two carbon atoms and four hydrogen atoms. It is commonly used as a chemical intermediate for the production of plastics and various other industrial applications. When ethene is burned, it produces a yellow, sooty flame due to incomplete combustion. This occurs because ethene has a double bond between the carbon atoms, which makes it less stable and prone to incomplete combustion. Therefore, ethene is a strong candidate for hydrocarbon Z.

Conclusion:
Based on the information provided, the hydrocarbon Z that burns with a yellow, sooty flame is most likely Ethene (C2H4). The presence of a double bond between the carbon atoms in ethene makes it less stable, leading to incomplete combustion and the formation of soot, resulting in a yellow flame.