A compound has the general formula X2O, with X representing an unknown element or Ion and O representing oxygen

. A compound has the general formula X2O, with X representing an unknown element or Ion and O representing oxygen. Which of the following could NOT be a name for this compound? Explain your answer. 
a. sodium oxide
b. iron(II)oxide
c. copper(I)oxide
d. dinitrogen monoxide
e. water

The Correct Answer and Explanation is:

The correct answer is: e. water

Explanation

To determine which compound could NOT have the formula X₂O, we need to understand how chemical formulas correspond to compound names based on chemical bonding and oxidation states.

The formula X₂O indicates that two atoms of an element or ion (X) are bonded to one atom of oxygen (O). Oxygen almost always has a −2 oxidation state, so the total negative charge from one oxygen atom is −2. Therefore, the two X atoms must each have a +1 charge (so +1 × 2 = +2), balancing the −2 from oxygen. This means that the compound X₂O is typically formed when X is a +1 cation.

Now let’s examine the options:

• a. Sodium oxide: Sodium (Na) is a Group 1 metal and forms Na⁺ ions. The formula Na₂O matches the X₂O pattern. ✅
• b. Iron(II) oxide: Iron(II) means Fe²⁺. To balance one O²⁻, only one Fe²⁺ is needed, giving the formula FeO, not Fe₂O. Therefore, Fe₂O (X₂O form) would correspond to Iron(I) oxide, which doesn’t exist. But iron(II) oxide is FeO, not Fe₂O. ❌ However, this answer is not the best option because we’re asked which compound name could NOT match X₂O — and iron(II) oxide is simply not X₂O, but it is a real compound.
• c. Copper(I) oxide: Copper(I) is Cu⁺. Two Cu⁺ ions would balance one O²⁻, making Cu₂O. This fits X₂O. ✅
• d. Dinitrogen monoxide: This is N₂O. Both nitrogen and oxygen are nonmetals. N₂O follows the X₂O formula. ✅
• e. Water: Water is H₂O, where hydrogen has a +1 charge, and there are two hydrogen atoms per one oxygen. This does NOT fit the formula X₂O, because X₂O implies two atoms of a heavier element (typically metals or larger nonmetals). Hydrogen is not typically symbolized as X, and H₂O does not follow the naming rules for “X₂O” types like metal oxides or covalent compounds. Water is a special case with a different naming convention. ❌✅

Conclusion: While both iron(II) oxide and water don’t match X₂O, the best answer is e. water, because it doesn’t correspond to any typical form of the X₂O compound structure and its naming convention is fundamentally different.