Final answer:
One mole of raindrops has a mass of approximately 3.0 x 10^22 g, and there are about 2.4 moles of raindrops in the Pacific Ocean, both rounded to two significant digits.
Step-by-step explanation:
To answer part (a) of the question, we first convert the mass of a single raindrop from milligrams to grams: 50 mg = 0.05 g. One mole of a substance contains Avogadro's number of entities (6.022 × 1023), so one mole of raindrops would have a mass of 0.05 g × 6.022 × 1023, which equals 3.011 × 1022 g. However, since we need to round to two significant digits, the mass of one mole of raindrops is roughly 3.0 × 1022 g.
For part (b), we convert the mass of the Pacific Ocean from kilograms to grams: 7.08 × 1020 kg = 7.08 × 1023 g. Next, we divide this by the mass of one mole of raindrops to find the number of moles: 7.08 × 1023 g / 3.0 × 1022 g/mol ≈ 2.36 moles. Again, rounding to two significant digits, the Pacific Ocean contains approximately 2.4 moles of raindrops.