What is formed when two different elements chemically unite?

When two different elements chemically unite, they form a compound. A compound is a substance created when two or more different types of atoms bond together in a fixed ratio. This chemical bond can be ionic or covalent, depending on the nature of the elements involved.

In contrast, a mixture consists of two or more elements or compounds that are physically combined but not chemically bonded, meaning they retain their individual properties and can be separated by physical means. A solution is a specific type of mixture where one substance (the solute) is dissolved in another (the solvent), also lacking the fixed composition and chemical bonding found in compounds. An element, on the other hand, is a pure substance that cannot be broken down into simpler substances by chemical means and consists of only one type of atom.

Thus, the correct answer reflects the fundamental chemical principle that compounds are the result of the chemical combination of different elements, resulting in substances with properties distinct from those of the individual elements.