Chemical formula of laughing gas is:

\(N_2O\)

The correct answer is option 2. \(N_2O\).

Laughing gas, scientifically known as nitrous oxide (\(N_2O\)), is a colorless, non-flammable gas with a slightly sweet odor and taste. It consists of two nitrogen atoms (N) bonded to one oxygen atom (O).

The structure of laughing gas (\(N_2O\)) can be represented as follows:

\[ \text{N} \equiv \text{N} - \text{O} \]

In this structure, there is a triple bond between the two nitrogen atoms and a single bond between one nitrogen atom and the oxygen atom. The arrangement of atoms in \(N_2O\) gives it a linear molecular geometry.

Nitrous oxide is commonly used as an anesthetic agent in dentistry and surgery due to its ability to induce euphoria and its analgesic (pain-relieving) properties. It is often referred to as "laughing gas" because of the euphoric effects it can produce when inhaled in small doses. Additionally, it is used as a propellant in whipped cream dispensers and in some racing cars to increase engine power.

The chemical formula \(N_2O\) accurately represents the composition of laughing gas, with two nitrogen atoms and one oxygen atom bonded together, making it the correct choice among the options provided.