10% of the atmosphere is located above the altitude where the pressure is

a. 100
b. 900

To determine the correct answer, you need to understand a concept known as "atmospheric pressure" and how it varies with altitude.

Atmospheric pressure refers to the force per unit area exerted by the weight of the air above a certain point in the Earth's atmosphere. As you move higher in altitude, the air molecules become less dense, resulting in lower atmospheric pressure.

Now, the question asks for the altitude above which 10% of the atmosphere is located. To find the answer, let's analyze the given options:

a. 100: This option implies that 10% of the atmosphere is located above an altitude of 100 units.

b. 900: This option suggests that 10% of the atmosphere is located above an altitude of 900 units.

To make a decision, we need to understand that the Earth's atmosphere is not uniformly distributed in terms of pressure or density with respect to altitude. In fact, the majority of the Earth's atmosphere is concentrated in the lower regions near the Earth's surface. The density and pressure decrease rapidly as we ascend to higher altitudes.

Considering this information, it is highly unlikely that only 10% of the atmosphere would be located above an altitude as low as 100 units. Therefore, option a can be ruled out.

However, option b, 900, seems plausible. At an altitude of around 900 units, the atmospheric pressure significantly decreases, and a substantial portion of the atmosphere might be located above that point. Hence, option b appears to be the more accurate answer.

To summarize, the correct answer is:

b. 900