Final answer:
The correct formula for calcium hydroxide is Ca(OH)₂, which represents one calcium ion paired with two hydroxide ions to balance the charges. The correct option is 1.
Step-by-step explanation:
The formula for calcium hydroxide is Ca(OH)₂. Calcium carries a +2 charge, represented as Ca²⁺, and thus requires two hydroxide ions (OH⁻) to balance its charge. Each hydroxide ion has a −1 charge, so two of them will balance out the +2 charge from the calcium ion.
When creating the chemical formula for an ionic compound that includes a polyatomic ion such as hydroxide, the polyatomic ion must be placed in parentheses if there is more than one of them within the compound. Therefore, the correct formula is written as Ca(OH)₂, where the subscript 2 indicates there are two hydroxide ions for every calcium ion, demonstrating a 1:2 ratio.
Hence, Option 1 is correct.