Which of the following substances forms a homogeneous mixture when mixed with water?

• A. NaCl
• B. Oil
• C. Sand
• D. Fe filings

Answer: (A)

Verified step by step guidance

1. Understand the concept of a homogeneous mixture: it is a mixture where the composition is uniform throughout, meaning the substances are completely dissolved or evenly distributed at the molecular level.
2. Consider the nature of each substance when mixed with water: NaCl (table salt) is an ionic compound that dissolves readily in water, forming a uniform aqueous solution.
3. Oil is nonpolar and does not mix well with polar water molecules, so it forms a separate layer, resulting in a heterogeneous mixture.
4. Sand is a solid particulate that does not dissolve in water and will settle at the bottom, creating a heterogeneous mixture.
5. Fe filings (iron particles) are solid metals that do not dissolve in water and will also settle or remain suspended, leading to a heterogeneous mixture.