**Question:** As per ISO, color of N20 cylinder is

A. Red
B. Green
C. Blue
D. Yellow

**Correct Answer:** D. Yellow

**Core Concept:**
The International Organization for Standardization (ISO) establishes standards for various industries, including medical gases like oxygen and nitrous oxide (N2O). These standards help in ensuring the safety, quality, and identification of these gases.

**Why the Correct Answer is Right:**
Nitrous oxide, also known as laughing gas, is a colorless and odorless gas. The ISO standard for identifying medical gases, specifically for nitrous oxide, is based on their color. Since nitrous oxide does not have a distinctive color, the standard assigns it a specific color based on its origin. Nitrous oxide is usually produced in a yellow cylinder through the oxidation of ammonia (NH3) to form nitric oxide (NO) and nitrogen (N2), which are then separated from each other. The yellow color is a result of the presence of nitric oxide.

**Why Each Wrong Option is Incorrect:**

A. Red - This color is typically used for oxygen (O2) and would not be appropriate for nitrous oxide.
B. Green - Green is not a standard color for nitrous oxide according to the ISO standard.
C. Blue - Blue is not a standard color for nitrous oxide according to the ISO standard.
D. Yellow (the correct answer) - Correctly represents the color of nitrous oxide, as mentioned above.

**Clinical Pearl:**
The ISO standard for medical gas identification helps prevent confusion and ensures patient safety by clearly distinguishing different gases used in medical settings. In this case, the correct color for nitrous oxide is yellow, helping healthcare professionals identify and use the correct gas when administering anesthesia or pain management.