**Core Concept**
The effective dose in radiation is measured in grays (Gy) and is a measure of the total energy deposited per unit mass of tissue. At a distance of 2 meters, the dose is 1 Gy, and we need to determine the dose at 1 meter.

**Why the Correct Answer is Right**
The dose rate decreases with the square of the distance from the radiation source. This is known as the inverse square law. Mathematically, this can be expressed as: dose ∝ 1/distance^2. Therefore, if the dose at 2 meters is 1 Gy, the dose at 1 meter will be 4 times greater (2^2 = 4). So, the dose at 1 meter would be 4 Gy.

**Why Each Wrong Option is Incorrect**
* **Option A:** This option is incorrect because it doesn't take into account the inverse square law. The dose would indeed increase, but not by a factor of 2, as the distance is halved.
* **Option B:** This option is incorrect because it suggests a decrease in dose, which is opposite to the expected result.
* **Option C:** This option is incorrect because it suggests a constant dose, which is not consistent with the inverse square law.

**Clinical Pearl / High-Yield Fact**
Remember the inverse square law when dealing with radiation exposure. The dose decreases with the square of the distance from the source.

**Correct Answer: B. 4 Gy**