Density of mixture from total mass over total volume

Steps:

• Mass of water: 1.5 m³ × 1000 kg m⁻³ = 1500 kg
• Mass of alcohol: 0.5 m³ × 800 kg m⁻³ = 400 kg
• Total mass: 1500 kg + 400 kg = 1900 kg
• Density: 1900 kg / 2 m³ = 950 kg m⁻³

Why D is correct:

• Matches formula ρ_mix = (total mass) / total volume, where masses add linearly and volume is given as 2 m³.

Why the others are wrong:

• A: 850 kg m⁻³ from incorrect equal-weight average ignoring volumes.
• B: 900 kg m⁻³ from volume-weighted densities without mass summation.
• C: 940 kg m⁻³ from arithmetic mean error, not total mass division.

Final answer: D