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 ethene to ethanal is catalysed by _______

$PdCl_2$

The correct answer is Option (2) → $PdCl_2$

Wacker process involves the oxidation of alkenes/alkynes to carbonyl compounds using palladium chloride as a catalyst.

Explanation of Options

Option 1: $TiCl_4$

Titanium tetrachloride is used in Ziegler–Natta catalysis for polymerization reactions, not in oxidation.

Option 2: $PdCl_2$

Palladium chloride is the key catalyst in the Wacker process. It helps convert ethyne into ethanal through oxidation.

Option 3: $MnO_2$

Manganese dioxide is used as an oxidizing agent in organic reactions but is not used in the Wacker process.

Option 4: $KMnO_4$

Potassium permanganate is a strong oxidizing agent but is not involved in this catalytic process.