Reaction monitoring via product volume and reactant concentration

Steps:

• Reaction consumes HCl, so its concentration decreases over time from initial value toward zero (or excess if present).
• Reaction produces H2 gas, so its volume increases from zero toward a maximum stoichiometric limit.
• Measurements at regular intervals yield curves: [HCl] declines nonlinearly; H2 volume rises nonlinearly to plateau.
• Correct graphs pair a decreasing [HCl]-time curve with an increasing H2 volume-time curve.

Why D is correct:

• Displays [HCl] decreasing and H2 volume increasing asymptotically, matching Le Chatelier's principle and integrated rate laws for reactant depletion and product accumulation.

Why the others are wrong:

• A: Shows linear changes, ignoring slowing rate as reactants deplete.
• B: Inverts curves (H2 decreasing, [HCl] increasing), contradicting reaction direction.
• C: Both curves plateau immediately, implying no reaction progress.

Final answer: D