Reaction Rate Factors Steps:

• Identify key factors: higher acid concentration increases rate; smaller Mg particles increase surface area and rate; higher temperature increases kinetic energy and rate.
• For lowest hydrogen production rate, favor low concentration, larger particles (less surface area), and lower temperature.
• Compare options: count net slowing effects relative to original conditions.
• Option C nets slowest rate with high concentration (speeds) but large particles and low temperature (both slow).

Why C is correct:

• It combines one rate-increasing change (higher concentration) with two rate-decreasing changes (larger particle size reduces surface area; lower temperature reduces collision frequency), per collision theory.

Why the others are wrong:

• A: Low concentration slows, but small particles and high temperature speed it more, netting faster rate.
• B: All changes (high concentration, small particles, high temperature) increase rate, producing fastest hydrogen output.
• D: Identical to C, but if distinct, lacks unique slowing factor (not enough information to differentiate).

Final answer: C