Units of equilibrium constant K_p based on Δn for gases Steps:

• Write the balanced reaction, noting all species are gases: H₂O₂(g) + Cl₂(g) → 2HCl(g) + O₂(g) (correcting apparent typos for balance).
• Count gaseous moles: 2 reactants (1 + 1), 3 products (2 + 1).
• Calculate Δn = moles products - moles reactants = 3 - 2 = 1.
• Units of K_p = Pa^{Δn} = Pa^1 = Pa.

Why B is correct:

• For Δn = 1, K_p = (P_{HCl}^2 P_{O_2}) / (P_{H_2O_2} P_{Cl_2}), so units Pa by the definition of K_p in terms of partial pressures.

Why the others are wrong:

• A: Applies if Δn = -1, like in ammonia synthesis.
• C: Applies if Δn = 2, like in some dissociations with larger mole increase.
• D: Applies if Δn = 0, like in reactions with equal gas moles on both sides.

Final answer: B