Which of the following is the correct chemical formula for aluminum selenide?

• A. AlSe2
• B. Al3Se2
• C. AlSe
• D. Al2Se3

Answer: (D)

Verified step by step guidance

1. Step 1: Identify the charges of the ions involved. Aluminum typically forms a +3 charge (Al³⁺), and selenium typically forms a -2 charge (Se²⁻).
2. Step 2: To write the correct formula, balance the total positive and negative charges so that the compound is electrically neutral.
3. Step 3: Use the crisscross method to balance the charges: take the magnitude of the charge on the aluminum ion (3) and use it as the subscript for selenium, and take the magnitude of the charge on the selenium ion (2) and use it as the subscript for aluminum.
4. Step 4: Write the formula using these subscripts: \(\mathrm{Al_2Se_3}\), which means 2 aluminum atoms and 3 selenium atoms combine to form aluminum selenide.
5. Step 5: Verify that the total positive charge (2 × +3 = +6) balances the total negative charge (3 × -2 = -6), confirming the formula is electrically neutral and correct.