When element 20A combines with element 8Y,

Step 1: Analyze the question We need to find the type of bond and the formula formed when element A (atomic number 20) combines with element Y (atomic number 8).

Step 2: Electron configurations

• A (Z = 20): 2, 8, 8, 2. It has 2 valence electrons, so it is a Group 2 metal (calcium).
• Y (Z = 8): 2, 6. It has 6 valence electrons, so it is a Group 16 non-metal (oxygen).

Step 3: Concept A metal combined with a non-metal forms an ionic (electrovalent) compound through electron transfer.

Step 4: Solution

• A loses 2 electrons: A → A²⁺ + 2e⁻
• Y gains 2 electrons: Y + 2e⁻ → Y²⁻
• The charges balance 1:1 (2+ and 2−), so the formula is AY (like CaO).

Step 5: Check the options

• A. Covalent AY: wrong, because a metal and a non-metal bond ionically.
• B. Ionic AY: correct.
• C. Ionic A₂Y: wrong, because it would need A⁺ ions.
• D. Covalent AY₂: wrong on both the bond type and the formula.

Tip: Find the valence electrons first, then decide the bond type. Metal + non-metal gives ionic. Next, write the ion charges and cross-check them to get the formula. For Group 2 combined with Group 16, the ratio is always 1:1, for example MgO, CaO, BaO.