2. What harmful change/s is/are brought about when a metal reacts or mixes with acids​

hydrogen gas

When metal reacts with acids it produces metal salt and hydrogen gas ( H2 ) . All metals do not react with acids to evolve hydrogen gas . Only those metals react which is more reactive than hydrogen . When metal reacts with acid it forms a salt which is basic in nature and releases hydrogen gas.

Explanation:

When metals react with other substances, the gradual wearing away or corrosion of a metal results.This may lead to deterioration of metals

explanation: it gains negative electrons, therefore becoming negatively charged. as charge cannot be created, nor destroyed, only transferred, this leaves the wool positive. now that they have opposite charges, the two items attract.

if you're asking what comes out, it's steam.