**Core Concept**
The refractive power of a lens is determined by its focal length, which is the distance between the lens and the point where parallel light rays converge. The refractive power of a lens is inversely proportional to its focal length.

**Why the Correct Answer is Right**
The refractive power of a lens is calculated using the formula: refractive power = 1 / focal length (in meters). Given that the focal length of the lens is 0.75 m, we can plug in this value to calculate the refractive power. The correct calculation yields a refractive power of 1.33 diopters (D).

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it does not take into account the focal length of the lens. Without knowing the focal length, we cannot accurately calculate the refractive power.
**Option B:** This option is incorrect because it suggests a negative refractive power, which is not possible for a lens in air. Lenses in air always have a positive refractive power.
**Option C:** This option is incorrect because it suggests a refractive power of 1.50 D, which is not consistent with the given focal length of 0.75 m.

**Clinical Pearl / High-Yield Fact**
Remember that the refractive power of a lens is inversely proportional to its focal length. This is a fundamental principle in optics that is essential for understanding how lenses work.

**Correct Answer:** D. 1.33 D