Number of air changes in one hour in a drawing room should be at least:

**Core Concept**
The question is related to ventilation requirements, specifically focusing on the number of air changes per hour in a drawing room. This concept is crucial in maintaining indoor air quality and preventing the accumulation of airborne pathogens or pollutants.

**Why the Correct Answer is Right**
To determine the correct answer, we consider the standard ventilation requirements. For a drawing room or similar spaces, a minimum of 2 air changes per hour is often recommended to ensure adequate removal of stale air and introduction of fresh air.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it suggests fewer air changes than the recommended standard.
**Option B:** This is not the correct minimum standard for air changes in such spaces.
**Option D:** This option exceeds the general recommendation for a drawing room, which is not typically necessary for such spaces.

**Clinical Pearl / High-Yield Fact**
A key point to remember is that ventilation standards can vary based on the specific use of a room, with higher air change rates required for areas like operating rooms or isolation wards.

**Correct Answer:** D. 2 air changes per hour.