An element is a substance that can not be broken down in simpler substances by chemical means. A compound is a substance that contains two or more substances that are chemically combined in a definite and fixed proportion by mass. A mixture is a combination of two or more substances which are not chemically combined. Mouthwash is an example of homogeneous mixture.
The element X is Copper.
Explanation :
Reactive metals from 3d transition series like Cu are very reactive because their standard reduction potential values are low.
Hence, when treated with a acid it tends to liberate hydrogen gas.
Also, because of its low reduction potential value, it can easily displace lead and tin from their salt solutions.
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