**Core Concept**
Daylight factor is a measure of the amount of daylight that enters a room, compared to the amount of daylight that enters a standard sky. It is an important consideration in architectural design, particularly in buildings that require natural lighting, such as homes and offices.

**Why the Correct Answer is Right**
The correct daylight factor is 2%, which is the minimum recommended for a living room. This means that 2% of the available daylight should enter the room. To achieve this, the room should have a large window or skylight that allows direct sunlight to enter, or a combination of windows and reflective surfaces to bounce natural light into the room. The daylight factor is calculated by comparing the amount of daylight entering the room to the amount of daylight entering a standard sky, which is assumed to be 100%.

**Why Each Wrong Option is Incorrect**
* **Option A:** This option is incorrect because it is not a valid daylight factor. Daylight factors can range from 0% (no daylight) to 100% (maximum daylight), but values above 2% are typically not necessary for a living room.
* **Option B:** This option is incorrect because it is too low for a living room. A daylight factor of 0.5% would result in a room that is very dimly lit, making it difficult to perform daily activities.
* **Option C:** This option is incorrect because it is too high for a living room. A daylight factor of 5% would result in a room that is very brightly lit, which may be uncomfortable and even cause eye strain.

**Clinical Pearl / High-Yield Fact**
A daylight factor of 2% is considered sufficient for a living room, but this value can vary depending on the specific lighting needs of the room and the surrounding environment. It is also worth noting that daylight factors can be influenced by factors such as window size, orientation, and shading devices.

**Correct Answer: D. 2%**