When magnesium is added to hydrochloric acid, a gas is formed. Explain what happens in the reaction, how the gas is collected and how it could be tested to prove what it is.

Explained below.

Explanation:

Formula when magnesium reacts with hydrochloric acid is given by;

Mg(s) + 2HCl(aq) = MgCl2(aq) + H2(g)

So, from the equation, we can see that the gas formed is hydrogen.

This hydrogen gas is collected by a method known as water displacement.

This gas can be tested for by holding a burning splint near to the top of the test container. The resulting effect should be a high pitched pop sound because the hydrogen gas will react with the oxygen gas in the air to result in a small explosion.

the tides are influenced by both the moon and the sun, it's easy to see that when the sun lines up with the moon and the earth, as during a new moon or full moon, the tidal effect is increased. these are known as spring tides, named not for the season, but for the fact that the water "springs" higher than normal. on the other hand, if the sun and the moon are 90 degrees apart in relation to an observer on earth as during the first quarter moon or third quarter moon, then high tides are not as high as they normally would be. this is because despite its greater distance, the sun's mass allows it to exert enough gravitational force on the oceans that it can negate some of the effects of the moon's pull. this phenomenon of lower high tides is called a neap tide. if you need more information on this topic visit moonconnection.com.

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.