The integrated circuits in your cell phone and computer are made from the semiconductor silicon. The silicon is obtained from a really inexpensive starting material, sand, which is primarily SiO2. One step in the purification of silicon is to separate it from solid impurities by forming the gas silicon tetrachloride.
Given the following reactions, what is the overall enthalpy change in converting 1.00 mol of silicon dioxide into pure silicon?

SiO2(s) + 2C(s) → Si(impure s) + 2CO(g); ΔH = +690 kJ
Si(impure s) + 2Cl2(g) → SiCl4(g); ΔH= -657 kJ
SiCl4(g) + 2Mg(s) → 2MgCl2(s) + Si(s); ΔH = -625 kJ

nanotechnology is a powerful tool in biomaterials research as it creates numerous possibilities for the engineering of functional molecules. nano-bio refers to projected ability to incorporate biomimicry into various materials at nanoscale.  

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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.

c) should be the answer.