Assertion: a material safe in bulk is necessarily safe as a nanopowder. Reason: its chemical composition is unchanged.
Answer: C
The composition is indeed the same, but size and surface chemistry decide where a particle can go in the body and how reactive it is once there. Each material must be assessed at each size rather than cleared by its bulk record.
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Comparing the crystallite size from Scherrer analysis with the hydrodynamic diameter from light scattering, the hydrodynamic figure is
Answer: D
Correct answer: larger, including the coating and solvation layer
Scherrer analysis of the X-ray line broadening measures the coherently diffracting crystalline domain, which may even be smaller than a polycrystalline particle. Light scattering measures the whole hydrodynamic entity, coating and associated solvent included. The hydrodynamic figure is therefore always the larger, and comparing the two is a useful check on the state of the dispersion.
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None of the following follows from quantum confinement except
Answer: A
Confining the carriers discretises and raises their energy levels, so the band gap and hence the emitted colour depend on size. Melting point depression, plasmon absorption and agglomeration all arise from surface effects instead.
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