Answer
$10^{4}$ viruses
Work Step by Step
Number of viruses = $\frac{10^{-9}V_{saliva}}{V_{virus}}=\frac{0.010cm^{3}}{10^{9}\times(\frac{4}{3}pi)\times(85nm/2)^{3}\times(10^{-7}cm/1nm)^{3}}=10^{4}$ viruses.
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