The compound formed between 14X and 16Y is _______?

Analyze the question: X and Y are written with numbers 14 and 16. In this kind of WASSCE question, these numbers are normally the atomic numbers (or group numbers in some versions). We need the formula of the compound they form.

Concept: Atoms combine to achieve a stable octet. The valency depends on the number of valence electrons, which you get from the electronic configuration.

Solution:

• X (atomic number 14): 2, 8, 4. It has 4 valence electrons, so it is in Group IV (this is silicon). Its valency is 4.
• Y (atomic number 16): 2, 8, 6. It has 6 valence electrons, so it is in Group VI (this is sulfur). It needs 2 more electrons, so its valency is 2.

Because X has 4 valence electrons and Y needs 2, they share electrons covalently (both are non-metals).

One X atom shares 4 electrons, and each Y atom takes 2 of them. So one X atom combines with two Y atoms:

X + 2Y → XY₂

Using valency crossover: X (valency 4) and Y (valency 2) give X₂Y₄, which simplifies to XY₂. This is like SiS₂, or CS₂ in the carbon analogue.

Checking the other options:

• A. XY would need equal valencies, which is not the case here.
• C. X₂Y would need X to have valency 1 and Y valency 2.
• D. X₄Y₆ does not match the valency ratio of 4:2, which is 2:1.

Answer: B. XY₂.

Tip: When a question gives numbers like these, write out the electronic configuration first (2, 8, 4 and 2, 8, 6), find the valencies, then cross them over and simplify. Always reduce the ratio to its lowest terms.