Final answer:
Magnesium and strontium are two elements that can best replace calcium in the experiment due to their similar chemical properties as alkaline earth metals.
Step-by-step explanation:
The two elements that can best replace calcium in the experiment are magnesium and strontium.
Magnesium is a good substitute for calcium because it is also an alkaline earth metal with similar properties. Both magnesium and calcium have two valence electrons and are in the same group of the periodic table, Group 2. Strontium, on the other hand, is another alkaline earth metal that can replace calcium due to its similar chemical properties.