Which of the following is the correct formula for a compound containing Al^{3+} and S^{2-} ions?

• A. Al_3S_2
• B. AlS_2
• C. AlS
• D. Al_2S_3

Answer: (D)

Verified step by step guidance

1. Identify the charges of the ions involved: aluminum ion is Al^{3+} and sulfide ion is S^{2-}.
2. Determine the ratio of ions needed to balance the total positive and negative charges so that the compound is electrically neutral.
3. Set up the equation for charge neutrality: (number of Al^{3+} ions) \times (+3) + (number of S^{2-} ions) \times (-2) = 0.
4. Find the smallest whole number ratio of Al^{3+} to S^{2-} ions that satisfies the charge neutrality condition. This involves finding the least common multiple of the charges 3 and 2.
5. Write the formula using the ratio found, placing the number of each ion as subscripts: Al_{2}S_{3}.