**Core Concept**
Malathion is an organophosphate insecticide widely used in household settings for vector control, particularly in malaria-endemic areas, due to its effectiveness against *Anopheles* mosquitoes.

**Why the Correct Answer is Right**
Malathion acts as a potent acetylcholinesterase inhibitor, disrupting nerve transmission in mosquitoes, leading to paralysis and death. It is specifically recommended by WHO and public health programs for indoor residual spraying (IRS) in malaria-prone regions. Malathion is stable, long-lasting, and effective against both adult and larval stages of *Anopheles* mosquitoes, making it ideal for household-level malaria prevention.

**Why Each Wrong Option is Incorrect**
Option B: Pyrethrum is effective against mosquitoes but is primarily used in insecticide-treated nets (ITNs) and sprays, not commonly used in household settings for routine malaria control.
Option C: Paris green (cupric acetate) is obsolete and toxic to humans; it has no role in modern malaria prevention.
Option D: Permethrin is used in ITNs and outdoor applications but is not typically used in household insecticide spraying for malaria.

**Clinical Pearl / High-Yield Fact**
Malathion remains a cornerstone of indoor residual spraying in malaria-endemic areas due to its proven efficacy and low cost—always used under trained supervision to avoid human exposure.

✓ Correct Answer: A. Malathion