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

The correct answer is option C, Mass

Mass is a constant quantity

Volume changes as ten vertical feet of original peat material becomes one vertical foot of coal

Area changes as the space occupied by the peat get reduced after squeezing

Density is mass/volume, since volume reduces, density increases.

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.