**Core Concept**
Pneumoconiosis refers to a group of lung diseases resulting from the inhalation of dust particles, leading to inflammation and fibrosis. The size and composition of the inhaled particles play a crucial role in determining the severity and type of pneumoconiosis.

**Why the Correct Answer is Right**
The correct answer is D. 1-5 μm because particles of this size are small enough to be retained in the lungs and cause inflammation and fibrosis. Particles within this range can penetrate deep into the lung tissue, causing damage to the alveoli and bronchioles. This size range is particularly hazardous because it allows the particles to evade the lung's natural defense mechanisms, such as mucociliary clearance.

**Why Each Wrong Option is Incorrect**
**Option A:** Particles ranging from 100-150 μm are too large to be inhaled deep into the lungs and are typically cleared by the upper respiratory tract. These particles are unlikely to cause pneumoconiosis.
**Option B:** Particles between 50-100 μm are also too large to penetrate deep into the lung tissue and are primarily cleared by the upper respiratory tract. While they may cause some irritation, they are unlikely to cause significant pneumoconiosis.
**Option C:** Particles ranging from 10-50 μm can be inhaled deep into the lungs, but they are still large enough to be cleared by the lung's natural defense mechanisms. These particles are less likely to cause pneumoconiosis compared to particles in the 1-5 μm range.

**Clinical Pearl / High-Yield Fact**
It's essential to remember that the size of the inhaled particles is a critical factor in determining the risk of pneumoconiosis. Particles smaller than 5 μm are particularly hazardous because they can penetrate deep into the lung tissue and cause significant inflammation and fibrosis.

✓ Correct Answer: D. 1-5 μm