• A. They are less dense near the top of the atmosphere • B. They are least dense in the atmosphere near sea level.

•C. They are evenly dense throughout the atmosphere.

• D. They are densest near the middle of the atmosphere.

In the diagram given in the attachement depicts the model of density of gas in the atmosphere.

The purple balls represent the gas molecules and we can see that the number of purple balls is more near the bottom i.e. Sea level and gradually decreased moving towards the top i.e increasing height or top of the atmosphere.

This shows that the density and pressure of the air decreases with increase in height.

So, the Correct Option is:

They are less dense near the top of the atmosphere.

And we are done !!

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