What is nitrous oxide commonly referred to as?

Nitrous oxide is commonly referred to as "laughing gas" primarily due to its use in medical and dental settings, where it is administered to patients to reduce anxiety and pain. When inhaled, nitrous oxide can create feelings of euphoria and relaxation, often leading to laughter during its effects, hence the name. This characteristic makes it popular for use in procedures that may otherwise cause discomfort or fear in patients.

The other terms in the options refer to different substances or concepts and do not accurately describe nitrous oxide. For instance, "rocket fuel" could refer to various propellants used in aerospace applications, while "chill gas" and "happiness gas" are not commonly used terms in scientific or medical contexts regarding nitrous oxide. The widespread recognition of nitrous oxide as "laughing gas" in both professional and public spheres underlines its definition and significance in relevant fields.