**Core Concept**
A standard mosquito net is designed to prevent the entry of mosquitoes and other disease-carrying insects into homes and sleeping areas. The number of holes per square inch is a critical factor in determining the net's effectiveness. A higher number of holes may allow more mosquitoes to pass through, while a lower number may hinder airflow and ventilation.

**Why the Correct Answer is Right**
The correct answer is 150 holes per square inch. This is because the World Health Organization (WHO) recommends a minimum of 150-156 holes per square inch for mosquito nets to be effective in preventing malaria and other vector-borne diseases. The mesh size and hole density are crucial in preventing mosquitoes from passing through, while allowing sufficient airflow and visibility.

**Why Each Wrong Option is Incorrect**
**Option A:** 100 holes per square inch is too low, as it may not provide adequate protection against mosquitoes and other insects. This density may allow more mosquitoes to pass through, reducing the net's effectiveness.

**Option C:** 250 holes per square inch is excessive, as it may compromise the structural integrity of the net. A higher hole density may weaken the net, making it prone to tears and holes.

**Option D:** 175 holes per square inch is closer to the recommended range, but it is still not the correct answer. The WHO recommendation is for a minimum of 150-156 holes per square inch, so 175 is slightly above the optimal range.

**Clinical Pearl / High-Yield Fact**
When selecting a mosquito net, look for one with a mesh size of 150-156 holes per square inch. This will provide adequate protection against mosquitoes and other disease-carrying insects, while allowing sufficient airflow and visibility.

**✓ Correct Answer: B. 150**