Which of the following compounds at 25°C and 1.0 atm contains an element in a +1 oxidation state?

• A. CO2
• B. MgO
• C. H2O
• D. NaCl

Answer: (D)

Verified step by step guidance

1. Understand what oxidation state means: It is the hypothetical charge an atom would have if all bonds to atoms of different elements were 100% ionic.
2. Analyze each compound to determine the oxidation states of their elements at 25°C and 1.0 atm:
3. For CO2: Carbon is bonded to oxygen. Oxygen usually has an oxidation state of -2. Since there are two oxygens, total charge from oxygen is -4, so carbon must be +4 to balance.
4. For MgO: Magnesium is a Group 2 metal, typically +2 oxidation state. Oxygen is -2. So Mg is +2, not +1.
5. For H2O: Hydrogen is usually +1, oxygen is -2. So hydrogen is +1 here, but the question asks for a compound containing an element in +1 oxidation state, so H2O qualifies as well.
6. For NaCl: Sodium is a Group 1 metal, almost always +1 oxidation state. Chlorine is -1. So Na is +1 here, which matches the question's requirement.