An element X with atomic number 12 forms a compound with element Y with atomic number 17. The formula of the compound formed is

According to the NCERT text, non-metals produce acidic oxides when dissolved in water, whereas metals give rise to basic oxides.

• Group 1 and Period 3 corresponds to Sodium ($Na$), which is an alkali metal. It forms a basic oxide ($Na_2O$).
• Group 2 and Period 3 corresponds to Magnesium ($Mg$), which is an alkaline earth metal. It forms a basic oxide ($MgO$).
• Group 16 and Period 3 corresponds to Sulfur ($S$), which is a non-metal. As demonstrated in Activity 3.8, burning sulfur powder produces sulfur dioxide ($SO_2$), which dissolves in water to form an acidic solution (sulfurous acid, turning blue litmus red). Thus, Group 16 and Period 3 is the most probable position for element X.
• Group 17 and Period 3 is Chlorine ($Cl$), which also forms acidic oxides, but Group 16 (Sulfur) is the primary representative non-metal studied in this chapter for oxide acidity.