How is the concentration of CO in the air exhaled from a smoker expressed as a percentage if it's 35 ppm?

To convert parts per million (ppm) to a percentage, you can use the relationship between these two units. One part per million means that there is one part of a substance in one million parts of the total mixture. Hence, to convert from ppm to a percentage, you divide the ppm value by 10,000.

In this case, if the concentration of carbon monoxide (CO) in the air exhaled from a smoker is 35 ppm, we perform the following calculation:

35 ppm = 35 / 1,000,000 = 0.000035

To express this as a percentage, multiply by 100:

0.000035 × 100 = 0.0035%

Therefore, the concentration of CO expressed as a percentage is 0.0035%. This numerical transformation clearly shows how ppm directly relates to a percentage, leading to the correct answer.