Consider the following reaction represented by the following equation: C$_2$H$_2$ $^{H_2}_{→}$ X  $^{H_2}_{→}$ Y.           X and Y respectively are?

Analyze the question: Ethyne (C₂H₂) reacts with hydrogen in two stages. We need to identify the product after each stage.

Concept: This is catalytic hydrogenation, which is an addition reaction. Each mole of H₂ added reduces the degree of unsaturation by one bond:

• Alkyne (triple bond) → alkene (double bond) → alkane (single bond)

Solution:

Step 1: Ethyne adds one mole of H₂ (catalyst such as Ni or Pd), and the triple bond becomes a double bond:

C₂H₂ + H₂ → C₂H₄ (X = ethene)

Step 2: Ethene adds another mole of H₂ (Ni catalyst, about 200°C), and the double bond becomes a single bond:

C₂H₄ + H₂ → C₂H₆ (Y = ethane)

So X = ethene and Y = ethane.

Checking the options:

• A. Reversed order, so wrong.
• B. Ethene and ethane, which is correct.
• C. Ethyne is the starting material, so it can't be a product.
• D. Ethane can't come first, and ethyne can't be a product of hydrogenation.

Tip: Remember the sequence of hydrogenation as -yne → -ene → -ane. Each H₂ added takes you one step down the series: ethyne → ethene → ethane. Adding hydrogen always means moving toward more saturated.