Peat deposits are found in waterlogged places where dead plant material piles up. when peat is buried, it undergoes compaction. it is subjected to heat and pressure for a long time, and a lot of water is squeezed out during this process. nearly ten vertical feet of original peat material becomes one vertical foot of coal. which of these remains unchanged in the system during the conversion of peat to coal? a) area b) density c) mass d) volume

Option C, Mass

Explanation:

The mass of a substance remains constant. Here the ten vertical feet of peat material consisted of only one vertical foot of substantial coal/carbon deposits the remaining nine vertical feet of peat material had water which drained out during compaction through the course of time.

Thus except mass, all three i.e volume, density and area of a ten vertical feet of peat deposits must have changed when the said quantity reduced to one vertical foot of peat.

Thus, option C is correct.

igneous rocks are formed by solidification of cooled magma (molten rock), with or without crystallization, either below the surface as intrusive (plutonic) rocks or on the surface as extrusive (volcanic) rocks.  

the composition depends on the source magma. there are almost a thousand types of composition found till now.  

hope this