Final answer:
The estimated mass of water on Earth is 1.5 × 1021 kg, which is approximately 1 × 1021 kg to 1 significant figure, so the correct answer is option c).
Step-by-step explanation:
The mass of water on Earth can be estimated using the volume and density of water. Given the volume of water is 1.5 × 1018 m³ and the density of water is 1.000 × 103 kg/m³, we can calculate the mass by multiplying the two:
m = volume × density = 1.5 × 1018 m³ × 1.000 × 103 kg/m³ = 1.5 × 1021 kg
Therefore, the estimated mass of water on Earth to 1 significant figure is 1 × 1021 kg, which corresponds to option c).