How is the concentration of these gases
increasing?

in case you mean greenhouse gases they are increasing due to the result of human activities in relation to fossil fuels. the concentration of greenhouse gases also increases due to deforestation. the concentration increases as more is entering the atmosphere than it is being removed.

i believe the answer is c. "baking" is the gerund, while "baking blueberry muffins" would be the gerund phrase. hope this ! : )

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.