This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Dental
Which of the following metal is considered as the principal hardener and gives red colour to the alloy? 
Select and explain. 
A. Platinum, B. Palladium, C. Copper, D. Zinc
C: Copper
Answer: C: Copper 
Explanation: Copper when added to gold-based alloys, imparts a reddish color to the gold and hardens the alloy via a solid-solution or ordered-solution mechanism.
Ref: Craig’s 14th edition page 183, 184