Question

read the text. then answer the question.
molecules of nitrogen (n₂) and oxygen (o₂) make up 99% of the gas particles in the atmosphere. the remaining gases are present at much smaller concentrations. measurements made in 2015, for example, showed that carbon dioxide (co₂) made up roughly 0.04% of the gas particles in the atmosphere.
the amount of a particular gas in the atmosphere can be expressed as a concentration with units of parts per million, or ppm. parts per million is a measurement of the number of particles out of every million particles. so, an atmospheric concentration of 1 ppm means that there is one particle of that gas out of every million particles of gases in the atmosphere. the atmospheric concentrations of some gases are so small that they are expressed in parts per billion or even parts per trillion.
complete the statement.
one hundred years ago, the atmospheric concentration of carbon dioxide was about 300 ppm, or about 0.03% of the gas particles in the atmosphere. in 2015, the atmospheric concentration of carbon dioxide was roughly ___ ppm.
300 350 400 450

Explanation:

Step1: Recall the relationship between percentage and ppm

We know that to convert a percentage to ppm, we can use the fact that \(1\% = 10000\) ppm (since \(1\%=\frac{1}{100}\) and \(1\) ppm \(=\frac{1}{1000000}\), so \(\frac{1}{100}\div\frac{1}{1000000} = 10000\)). Alternatively, we can use the proportion: if \(x\%\) is the percentage, then the ppm is \(x\times10000\) (because \(\frac{\text{ppm}}{1000000}=\frac{\text{percentage}}{100}\), so \(\text{ppm}=\text{percentage}\times\frac{1000000}{100}=\text{percentage}\times 10000\)).

Step2: Convert 0.04% to ppm

Given that in 2015, the percentage of \(CO_2\) is \(0.04\%\). Using the formula \(\text{ppm}=\text{percentage}\times 10000\), we substitute the percentage value:
\(\text{ppm}=0.04\times10000 = 400\)

Answer:

400