Which gas commonly used in medicine and anaesthesia is popularly known as "laughing gas"?

Introduction / Context:
Several nitrogen oxides exist in the atmosphere and in industrial and medical applications. One of them, nitrous oxide, is widely known by the common name laughing gas because of its characteristic effect on mood and perception when inhaled in controlled conditions. This question asks you to connect that popular term with the correct chemical species from among several similar sounding nitrogen compounds. Such questions test both chemical nomenclature and general awareness of medical and industrial uses of gases.

Given Data / Assumptions:
- The question mentions a gas called laughing gas, known for its characteristic effects on humans.
- Four nitrogen containing gases are listed as options: nitrous oxide, nitrogen, nitric oxide, and nitrogen peroxide.
- Only one of these is popularly called laughing gas in textbooks and common usage.
- Standard chemical naming conventions are assumed for the given compounds.

Concept / Approach:
Nitrous oxide has the chemical formula N2O and is a colourless gas with a slightly sweet odour and taste. When inhaled in small controlled amounts, it can produce a feeling of euphoria and laughter, which gave rise to the name laughing gas. It is used as an anaesthetic and analgesic in dentistry and minor medical procedures, and also appears in some industrial applications. The other listed gases, such as nitrogen (N2), nitric oxide (NO), and nitrogen peroxide (commonly nitrogen dioxide NO2 or dinitrogen tetroxide N2O4), do not have this effect and are not known by this nickname. Therefore we identify nitrous oxide as laughing gas.

Step-by-Step Solution:
Step 1: Recall that laughing gas is a common name used in both chemistry and medicine for a particular nitrogen oxide. Step 2: Remember that this gas has the formula N2O and the systematic name nitrous oxide. Step 3: Compare with nitrogen, which is diatomic N2 and is a major component of air but is chemically inert under normal conditions and does not cause laughter. Step 4: Compare with nitric oxide, NO, which plays roles in biological signalling and environmental chemistry but is not used as an anaesthetic under the name laughing gas. Step 5: Compare with nitrogen peroxide, a less precise name usually related to nitrogen dioxide or its dimer, which are toxic pollutants and certainly not laughing gas. Step 6: Conclude that nitrous oxide is the only option that matches the common name laughing gas.

Verification / Alternative check:
A quick check in any basic chemistry or general science textbook lists nitrous oxide as laughing gas and notes its use in dental anaesthesia. Descriptions highlight its mild anaesthetic and analgesic properties along with its ability to induce temporary euphoria and laughter. More advanced references also describe its environmental role as a greenhouse gas. None of these references ever call nitrogen, nitric oxide, or nitrogen dioxide by the name laughing gas. This literature cross check confirms that nitrous oxide is the correct and widely accepted answer.

Why Other Options Are Wrong:
Nitrogen: This is a chemically inert diatomic gas that forms the bulk of the atmosphere and does not have anaesthetic or laughing effects.
Nitric oxide: Although biologically important, it is not used as laughing gas and can be harmful at high concentrations.
Nitrogen peroxide: This term usually refers to nitrogen dioxide related species which are toxic air pollutants, not anaesthetic gases used for medical purposes.

Common Pitfalls:
Candidates sometimes confuse nitrous oxide with nitric oxide because their names sound similar. Remember that nitrous oxide has two nitrogen atoms and one oxygen atom, while nitric oxide has one nitrogen and one oxygen. Another error is to assume that any nitrogen based gas used medically might be laughing gas, without recalling the specific name and formula. A good strategy is to memorise a small set of important gas nicknames, such as laughing gas for nitrous oxide, tear gas for certain irritant gases, and marsh gas for methane, and link them with their correct formulas and uses.

Final Answer:
The gas popularly known as laughing gas is Nitrous oxide, which has the chemical formula N2O and is used as a mild anaesthetic and analgesic.