🔍 Key Concepts

• Meaning of ppm (parts per million) as a ratio, not a specific unit like ounces or pounds • How units must be consistent on top and bottom of the ratio • Relationship between different ways to express the same fraction (e.g., 8 parts per 1,000,000 vs scaled-up versions)

💭 Think About

• What does 8 ppm literally mean in terms of "parts of oxygen" to "parts of water"? • If ppm is a ratio, can you use any units you want for oxygen and water, or do they need to match in some way? • Look at each answer: which ones keep the same type of units in the numerator and denominator so the ratio actually means "parts per million"?

✅ Before You Answer

• Confirm that ppm = parts of solute / 1,000,000 parts of solution, using the SAME kind of unit (mass with mass, or volume with volume). • Check each choice to see whether the unit on top and bottom match (both mass or both volume). • Verify which choice keeps the 8-to-1,000,000 relationship without changing it to 80-to-100,000 or mixing tons with pounds/ounces.