Complete the statement.
Calcium is ().

 - a compound
 - an elementary substance
You can tell whether calcium is an elementary substance or a compound by counting the number of atomic symbols in its chemical formula. An atomic symbol consists of either one capital letter or a capital letter followed by one or two lowercase letters.
The chemical formula for calcium contains one atomic symbol: Ca. So, the formula tells you that calcium is composed of only one chemical element.
Since calcium is composed of only one chemical element, calcium is an elementary substance.