The formation of oxide layer on metals follows first order kinetics and completely stops when the oxide thickness becomes 10 nm. If one hour after exposure of oxygen to metal surface the thickness is 7.5 nm, then what would be the thickness 120 minute after the exposure?

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10 nm

8.475 nm

5.25 nm

9.375 nm

answer is D.

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Detailed Solution

One hour after exposure of oxygen to metal surface the thickness is 7.5 nm,

$\begin{array}{l} 1 \times k = \ln (\frac{10}{2.5}) \end{array} k = \ln (\frac{10}{2.5})$

Now, thickness after 120 minute or 2 hours the exposure,

$2 \times k = \ln [\frac{10}{10 - τ}] \Rightarrow τ = 9.375 nm$

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