What is the equivalent percentage of 400ppm?

To convert parts per million (ppm) to a percentage, you can use the relationship that 1 ppm is equal to 0.0001%. This is based on the notion that 1 ppm means 1 part of a substance in one million parts of the total solution or mixture.

To find the percentage equivalent of 400 ppm, you multiply by the conversion factor:

400 ppm × 0.0001%/ppm = 0.04%.

This calculation shows that 400 ppm is equal to 0.04%, which reflects a very small fraction of the total mixture. Thus, the correct answer is indeed the percentage represented by 400 ppm.