Which of the following gases is referred to as ‘laughing gas’?

The correct answer is option 4. Nitrous Oxide.

The gas referred to as "laughing gas" is Nitrous Oxide.

Nitrous oxide (\(N_2O\)) is commonly known as "laughing gas." It earned this nickname due to its euphoric effects when inhaled in small doses. It is sometimes used as a mild anesthetic or sedative in medical and dental procedures, where it can induce feelings of euphoria and relaxation.