Which of the following does not involve Pt as catalyst?

(A) contact process for making $H_2SO_4$.
(B) Ziegler-Nata catalyst.
(C) Adams catalyst, used for reduction.
(D) catalyst to decompose $KClO_3$ to give $O_2$.

Choose the correct answer from the options given below:

(A), (B) and (D) only

The correct answer is Option (3) → (A), (B) and (D) only

• (A) Contact process for making H₂SO₄: Historically used platinum, but modern/industrial process uses vanadium pentoxide (V₂O₅) to avoid poisoning. In many standard contexts (especially exams), it is considered as not using Pt currently.
• (B) Ziegler-Natta catalyst: Uses titanium halides (e.g., TiCl₄ or TiCl₃) with organoaluminum compounds (e.g., AlEt₃). No platinum.
• (C) Adams catalyst, used for reduction: This is platinum dioxide (PtO₂), which reduces to platinum black during hydrogenation reactions. Involves Pt.
• (D) Catalyst to decompose KClO₃ to give O₂: Uses manganese dioxide (MnO₂). No platinum.

Thus, the options that do not involve Pt are (A), (B), and (D).