Answer:
Strontium, as opposed to other elements on the periodic table (with the exception of others in the same group/column i.e., the vertical direction), is a good substitute for Calcium because they are in the same group.
Explanation:
This is because elements of the same group behave similarly and have similar properties. This is due to the fact that elements of the same group (in the vertical direction) have the same number of valence electrons.