Concept: HCF: HCF or Highest Common Factor is the greatest number which divides each of the two or more numbers. Calculation: Number of gold coins = 75 Number of silver coins = 120 Maximum number of coins can be placed = HCF of 75 and 120 ⇒Factors of 75 = 5 × 5 × 3 ⇒ Factors of 120 = 2 × 2 × 2 × 3 × 5 ⇒ HCF of 75, 120 = 15 ∴ Maximum number of coins that each stack = 15 ∴ Option c is correct.