Solution A has a mass of 70 g. Solution B has a mass of 35 g. When they are mixed, a chemical reaction occurs in which a gas is produced. If the mass of the final mixture is 90 g, what mass of gas was produced?

 Mass of gas produced : 15 g

In general, the reaction takes place in the open air. If the reaction results in the form of gas as in combustion, the mass of the reaction results will be smaller than the original mass.  

Conservation of mass applies to a closed system, where the masses before and after the reaction are the same

So In a closed/isolated system, the total mass of the substance before the reaction will be equal to the total mass of the reaction product.

Mass of solution A  = 70 g

Mass of solution B = 35 g

Mass of mixture : 90 g

Mass of gas : X

Mass of gas X :

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.

d

explanation: