The reactions of high molecularity are rare, because

Of very large activation energy of many bodies
Of low probability of many body collisions
Many body collisions are not favoured energetically
Of requirement of very large concentration for such reactions
✅ The correct answer is option B.

For a heterogenous catalytic reaction, A + B → C, with equimole feed of A and B, the initial rate – rA0 is invariant with total pressure. The rate controlling step is

Surface Kc/(1 + TS) reaction between absorbed A and B in the gas phase
Surface reaction between absorbed A and absorbed B
Surface reaction between A in the gas phase and absorbed B
Desorption of C
✅ The correct answer is option D.