Read the passage carefully and answer the questions.
The transition metals and their compounds are known for their catalytic activity. This activity is ascribed to their ability to adopt multiple oxidation states and to form complexes. Vanadium(V) oxide (in Contact Process), finely divided iron, and nickel (in Catalytic Hydrogenation) are some of the examples. Catalysts at a solid surface involve the formation of bonds between reactant molecules and atoms of the surface of the catalyst (first row transition metals utilise 3d and 4s electrons for bonding). This has the effect of increasing the concentration of the reactants at the catalyst surface and also weakening of the bonds in the reacting molecules (the activation energy is lowering). Also because the transition metal ions can change their oxidation states, they become more effective as catalysts.
In the Wacker process the oxidation of ethyne to ethanal is catalysed by _______
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → \(PdCl_2\)
In the Wacker process, an alkene is oxidised by air to a carbonyl compound in aqueous solution, with palladium(II) chloride as the catalyst and copper(II) chloride to regenerate it. Ethene gives ethanal:
\( \displaystyle \ce{2CH2=CH2 + O2} \xrightarrow[\ce{H2O}]{\ce{PdCl2},\ \ce{CuCl2}} \ce{2CH3CHO} \)
Palladium(II) oxidises the alkene and is reduced to palladium metal; copper(II) chloride oxidises the palladium back to palladium(II), and air oxidises the copper(I) formed back to copper(II). So the catalyst for the oxidation to ethanal is \( \ce{PdCl2} \).
Note 1: It seems that there is a mistake in the original NTA paper, which prints “oxidation of ethyne to ethanal” when it should read “oxidation of ethene to ethanal”. The NCERT textbook prints the same slip in this sentence; the Wacker process oxidises ethene, as in the equation above.
NCERT (2026-27 edition):
Some Applications of d- and f-Block Elements – “… Many of the metals and/or their compounds are essential catalysts in the chemical industry. V2O5 catalyses the oxidation of SO2 in the manufacture of sulphuric acid. TiCl4 with Al(CH3)3 forms the basis of the Ziegler catalysts used to manufacture polyethylene (polythene). Iron catalysts are used in the Haber process for the production of ammonia from N2/H2 mixtures. Nickel catalysts enable the hydrogenation of fats to proceed. In the Wacker process the oxidation of ethyne to ethanal is catalysed by PdCl2.”
Note 2: The same/similar question has been asked in different years by NTA as per the details given below:
| 2026 | 2025 | 2024 | 2023 | 2022 |
|---|---|---|---|---|
| 24-05 S2 | 21-05 S2 | – | – | – |