Answer:
C.) Calcium
Step-by-step explanation:
Because none of the answer choices are nonmetals, we can safely assume this compound is not covalent. This means that the atoms involved in this molecule were ions before they bonded.
Chlorine, located in the 17th column, typically ionizes to become the anion Cl⁻. This anion has a negative charge of -1. The subscript indicates that there are 2 chorine ions in the compound, increasing the overall negative charge to -2 (2 x -1 = -2).
Since ionic compounds are neutral, the correct answer choice is the atom that ionizes to form a cation that can make the overall charge of the compound 0. As such, the cation needs to have a positive charge of +2 (+2 + (-2) = 0).
Aluminum = Al³⁺
Sodium = Na⁺
Calcium = Ca²⁺
Argon = does not typically ionize
Therefore, calcium must be the unknown element (X), making the compound CaCl₂.