If one were 230 kilometers above sea level, one would be in the part of the atmosphere known as the

The Earth's atmosphere consists of 6 layers going up. 

Troposhere is the closest layer. From the Earth's surface it extends up into the atmosphere about 8-15 meters.

Stratosphere extends above the troposphere about 50 km from the ground. 

Above the stratosphere is the Mesosphere which goes up to 85 km above the surface of the Earth.

Then we have the Thermosphere which goes up to 500 to 1,000 km above ground. 

The Exosphere, which extends from the thermosphere to about 100,000km to 190,000 km.

The ionosphere is a layer that is not exactly as distinct as the others. It overlaps the mesosphere and exosphere. 

Now if you were 230 kilometers above sea level, then you would be in the 4th layer of the atmosphere, or the Thermosphere because it starts at about 86 km above sea level and extends to about 500 to 1,000 km above sea level.

The answer is d) by requesting advice on science internet sites