**Core Concept**
In forensic medicine, the level of coproporphyrin in urine is a significant indicator of lead poisoning or other heme pathway disorders. The normal range of coproporphyrin in urine is crucial for differentiating between exposed and nonexposed individuals.

**Why the Correct Answer is Right**
The normal range of coproporphyrin in urine for nonexposed individuals is less than 150 microgram/litre. This is because coproporphyrin is a byproduct of the heme biosynthetic pathway, and its levels are tightly regulated in the body. When individuals are exposed to lead or other heme pathway disruptors, the levels of coproporphyrin in urine increase significantly. Therefore, a level of less than 150 microgram/litre is indicative of nonexposure.

**Why Each Wrong Option is Incorrect**
**Option B:** This option is incorrect because a level of less than 1000 microgram/litre is still within the normal range for exposed individuals, not nonexposed ones.

**Option C:** This option is incorrect because a level of more than 500 microgram/litre is indicative of exposure to lead or other heme pathway disruptors, not nonexposure.

**Option D:** This option is incorrect because option A (less than 150 microgram/litre) is indeed the correct answer, making option D an incorrect choice.

**Clinical Pearl / High-Yield Fact**
It's essential to remember that the level of coproporphyrin in urine is a sensitive indicator of lead poisoning, and levels above 150 microgram/litre can indicate exposure, even at low concentrations.

**✓ Correct Answer: A. Less than 150 microgram/litre**