Answer:
C. Varieties of an element that differ only in the number of neutrons are called isotopes.
Explanation:
The Earth is approximately old. The solar system formed from giant gas clouds which was a part of the solar nebula.
The surface of soil which demarcates two soils of different geological ages is called a unconformity.
Palesol is the soil that lies between sediments or volcanic deposits. If the paleosol is older they have lithified rock.
Hence, option C is true.