Complete the statement.
Phosphine is ().
A: a compound
B: an elementary substance
You can tell whether phosphine is an elementary substance or a compound by counting the number of symbols in its chemical formula. A symbol contains either one capital letter or a capital letter followed by one or two lowercase letters.
The chemical formula for phosphine is PH3. This formula contains two symbols: P for phosphorus and H for hydrogen. So, the formula tells you that phosphine is made of two chemical elements bonded together.
Substances made of two or more chemical elements bonded together are compounds. So, phosphine is a compound.