Which of the following is not a product of acid and metal reactions?

In reactions between acids and metals, the typical products formed include a salt and hydrogen gas. The general reaction can be summarized as:

[ \text{Acid} + \text{Metal} \rightarrow \text{Salt} + \text{Hydrogen gas} ]

In this context, when an acid reacts with a metal, the metal displaces hydrogen from the acid, resulting in the formation of a salt (the metal ion from the metal combines with the anion from the acid) and hydrogen gas, which is evolved during the reaction.

Water is often produced in other types of acid-base reactions, particularly those involving bases or neutralization reactions, but it is not a direct product of the reaction between a simple metal and acid. Therefore, the presence of water in other contexts does not affect the fundamental understanding of the metal-acid reaction products.

Carbon dioxide, while a product of some acid reactions (such as those involving carbonates or bicarbonates reacting with acids), is not produced when a metal reacts directly with an acid. Thus, the only products you would expect from a straightforward acid and metal reaction are salt and hydrogen gas, confirming that carbon dioxide is not a product of this particular reaction type.