1. The problem asks for the formula of the compound formed between element Y and aluminum, given that Y forms Na2Y. 2. From Na2Y, we see that Y has a charge of -2 because sodium (Na) has a charge of +1 and there are two sodium atoms balancing one Y atom. 3. Aluminum (Al) typically forms a +3 charge ion, Al^{3+}. 4. To form a neutral compound between Y^{2-} and Al^{3+}, we need to balance the total positive and negative charges. 5. The least common multiple of 2 and 3 is 6, so we need 3 Y^{2-} ions (3 × -2 = -6) and 2 Al^{3+} ions (2 × +3 = +6) to balance the charges. 6. Therefore, the formula of the compound is Al2Y3. Final answer: $$\mathrm{Al_2Y_3}$$