Combustion, or , is an example of one of the most familiar chemical changes. melting of ice, likewise, is one of the most common examples of physical changes. when a piece of coal burns, combines with the carbon in the coal. the products are carbon dioxide gas, water vapor, and a lot of ash. after careful measurements are taken, the of the reactants (coal and oxygen) is to the mass of the products (carbon dioxide, water vapor, and ash). during the reaction, the quantity of matter is unchanged. similarly, when 10 grams of ice , grams of water is obtained. mass is in this change as well.'

specific gravity is the density of a substance divided by the density of water. since (at standard temperature and pressure) water has a density of 1 gram/cm3, and since all of the units cancel, specific gravity is usually very close to the same value as density

so "c" is the answer

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definition

                    entropy is a measure of the randomness or the extent of disorder of a chemical process.

                      enthalpy is a measure of the heat change of a reaction occurring at a constant pressure.

measurement units:

                        entropy is measured in joule per kelvin (jk⁻¹)   whereas enthalpy is measured in joule per mole (jmol⁻¹)

requirements:

                            entropy has no requirements or limits, and its change is measured by the division between the heat change of the chemical process and the temperature.

                              in contrast, enthalpy can only be related to the heat change of the reaction under standard conditions.