if an element X with atomic number 13 combines with an element Y whose atomic number is 8 the most likely formula of the compound formed between X and Y is?

Step 1: Analyze the question We need the formula of the compound formed by element X (atomic number 13) and element Y (atomic number 8).

Step 2: Electronic configurations

• X (Z = 13): 2, 8, 3. It has 3 valence electrons, so it loses 3 electrons to form X³⁺. This is aluminium.
• Y (Z = 8): 2, 6. It has 6 valence electrons, so it gains 2 electrons to form Y²⁻. This is oxygen.

Step 3: Balance the charges (criss-cross method)

• X has a charge of +3 and Y has a charge of -2.
• Cross the numbers: X gets the 2 and Y gets the 3.
• The formula is X₂Y₃, which is Al₂O₃.

Check: 2 × (+3) = +6 and 3 × (−2) = −6, so the total charge is zero.

Answer: The formula is X₂Y₃, which is option E.

Tip: For ionic compounds, find each element's valency from its valence electrons. Metals lose electrons and non-metals gain them. Then criss-cross the valencies to get the formula. Al₂O₃ is a very common example in exams, so remember it.