Final answer:
Acetylene is actually heavier than air and has a faint odor. It is a colorless gas used in welding torches for its high heat of combustion. Its density and flammability make it important in metalworking, though it must be handled with care.
Step-by-step explanation:
The statement that acetylene is colorless, odorless, and lighter than air is false. In fact, acetylene (C₂H₂) is a colorless gas and it does have a faint odor. More importantly, it is not lighter than air; its density is 1.171 kg/m³ at standard temperature and pressure (STP), making it slightly heavier than air, which has an average density of about 1.225 kg/m³.
Acetylene is known for its high flammability and is widely used as a fuel for welding torches due to its high heat of combustion. It takes advantage of this property to produce a flame hot enough to melt and join metals. Acetylene is composed of 92.3% carbon and 7.7% hydrogen by mass, and its empirical formula can be calculated based on this composition. It plays a vital role in metalworking industries and requires careful handling due to its combustive properties.