**Core Concept**
The question tests the understanding of the inverse square law, which describes how the intensity of radiation varies with distance. In radiography, this law is crucial for determining the correct exposure times and techniques to achieve optimal image quality.

**Why the Correct Answer is Right**
When the source film distance (SFD) increases, the intensity of the radiation decreases. According to the inverse square law, the intensity of radiation is inversely proportional to the square of the distance from the source. Therefore, if the distance is doubled (from 8 inches to 16 inches), the intensity of radiation will decrease to one-fourth of its original value. To compensate for this decrease, the exposure time must be increased to allow for the same amount of radiation to reach the film.

**Why Each Wrong Option is Incorrect**
* **Option A:** This option would imply that the exposure time remains the same, which contradicts the inverse square law.
* **Option B:** This option suggests that the exposure time decreases, which is incorrect because the intensity of radiation decreases with increased distance.
* **Option D:** This option implies an increase in exposure time that is not proportional to the increase in distance, which is also incorrect.

**Clinical Pearl / High-Yield Fact**
The inverse square law is essential for determining the correct exposure times and techniques in radiography. Remember that the intensity of radiation decreases with increased distance, and exposure times must be adjusted accordingly to achieve optimal image quality.

**Correct Answer: C. 2 seconds.**