Complete the statement.
Hydrogen fluoride is ().

 - a compound
 - an elementary substance
You can tell whether hydrogen fluoride 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 hydrogen fluoride, HF, contains two atomic symbols: H for hydrogen and F for fluorine. So, the formula tells you that hydrogen fluoride is composed of two chemical elements bonded together.
Since hydrogen fluoride is composed of multiple chemical elements bonded together, hydrogen fluoride is a compound.