What is the correct formula of calcium hydroxide?

$Ca(OH)_{2}$

The correct answer is option 4. $Ca(OH)_{2}$.

Certainly! Calcium hydroxide is a chemical compound composed of calcium (Ca), one calcium atom, and hydroxide (OH) groups. The hydroxide ion is made up of one oxygen atom and one hydrogen atom. The correct formula for calcium hydroxide is determined by the charges on the ions and the need for electrical neutrality in the compound.

Here is the breakdown:

1. Calcium Ion (Ca²⁺):

Calcium loses two electrons to attain a stable electron configuration, resulting in a 2+ charge (Ca²⁺).

2. Hydroxide Ion (OH⁻):

The hydroxide ion carries a 1- charge due to the extra electron.

To balance the charges and achieve a neutral compound, one calcium ion (Ca²⁺) combines with two hydroxide ions (OH⁻). Therefore, the correct formula is \( \text{Ca(OH)}_2 \), indicating one calcium atom bonded to two hydroxide ions.

So, the correct answer is option 4. \( \text{Ca(OH)}_2 \).