Blood serum in healthy adults normally contains approximately 3.2 mg/ml of sodium ions (na+) and approximately 3.5 mg/ml of chloride ions (cl−).
how many milliliters of blood serum would be needed to obtain 3.1 g of na+?
how many milliliters of blood serum would be needed to obtain 3.1

968.75 mL of blood serum are needed to obtain 3.1 g of Na⁺

885.71 mL of blood serum are needed to obtain 3.1 g of Cl⁻

Explanation:

Knowing that the blood serum contains 3.2 mg/mL of sodium ions (Na⁺) we devise the following reasoning:

if          3.2 mg of sodium ions are found in 1 mL of blood serum

then    3100 mg of sodium ions are found in X mL of blood serum

X = (1 × 3100) / 3.2 = 968.75 mL

Knowing that the blood serum contains 3.5 mg/mL of chlorine ions (Cl⁻) we devise the following reasoning:

if          3.5 mg of chlorine ions are found in 1 mL of blood serum

then    3100 mg of chlorine ions are found in X mL of blood serum

X = (1 × 3100) / 3.5 = 885.71 mL

the answer is b because, investigating whether another species of moth also drinks tears might be interesting, but it would not directly explain why this species of moth does.

to explain why this species of moth drinks tears, the scientist could ask: "what nutrients that moths need are in elephant tears? "

the scientist could experiment with moth repellent or oter ways to keep the moths away, but that would not answer his original question.