Which of the following is known as ammonia?

NH₃

The correct answer is option 1. \(NH_3\).

\(NH_3\) is the chemical formula for ammonia, a colorless gas with a pungent odor. It is widely used in various applications like fertilizers, refrigerants, and as a cleaning agent.

\(PH_3\) is the formula for phosphine, a colorless gas with a garlic-like odor. It is a highly toxic compound.

\(NO_3\) is the formula for the nitrate ion, a polyatomic ion commonly found in salts like potassium nitrate \((KNO_3)\) and sodium nitrate \((NaNO_3)\).

\(NO_2\) is the formula for nitrogen dioxide, a reddish-brown gas with a pungent odor. It is a major air pollutant.

Therefore, based on the chemical formulas, NH3 is the only option corresponding to ammonia.