Competency #7
Answer and Explanation
The correct answer is D.
The compound Ca(OH)2 contains Ca2+ and OH- ions (with twice as many of the latter).
A compound is generally formed from 2 types of ions (one positive, one negative). We can therefore eliminate the first two choices from consideration.
When you see a compound containing 3 ore more types of atoms, consult a table of polyatomic ions. Look for a group of atoms in the compound that is the same as one of the polyatomic ions. In this case, we see the hydroxide ion, OH-, on the table of polyatomic ions and in the compound we are analyzing. The subscript ‘2' in our compound means that there are twice as many OH- ions as there are calcium ions.
Since Ca is in the column IIA of the periodic table, we know neutral Ca has 2 electrons in its outer shell. It often loses (gives away) those 2 electrons to achieve a more stable electron configuration. In doing so, calcium forms a Ca2+ ion.