The formula of the compound potassium iodide, which crystallizes with a cubic unit cell containing iodide ions at the corners and a potassium ion in the center, is KI.
The formula of a compound is determined by the arrangement of its constituent atoms or ions. In the case of potassium iodide, it is mentioned that iodide ions are present at the corners of the cubic unit cell, while a potassium ion is located at the center.
To determine the formula of the compound, we need to consider the ratio of the ions present in the unit cell. Since there is only one potassium ion in the center of the unit cell, and there are eight corners, each occupied by an iodide ion, we can write the formula as KI.