A sample of an element has a mass of 80.01g and a density of 2.70 g/cm3. How many significant figures does the mass have?

The mass has 4 significant figures

Rules for significant numbers

a sample has mass = 80.01 g

a zero which is located between two non-zero numbers including a significant number, so the mass has 4 significant figures : 8,0,0 and 1

answer is: c. the experiment shows that the red substance experienced a chemical change.

this is chemical change (chemical reaction), because two new substances are formed (metalig liquid and gas), the atoms are rearranged and the reaction is followed by an energy change.

this is example of chemical decomposition.

chemical decomposition (analysis) is the separation of a single chemical compound into its two or more elemental parts or to simpler compounds.  

chemical decomposition is opposite of chemical synthesis.

by cartels in other countries, shipped by air, mail, or land. i cant really see your answer choices : /