The lowest pressure (the best vaccum) that can be created in laboratory at 20∘C is 10−10mm of Hg. At this pressure, the number of ideal gas molecules per cm3 will be :
A
3.22×1012
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B
1.61×1010
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C
3.22×108
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D
3.29×106
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Solution
The correct option is D3.29×106 Given : P=10−10mm of Hg=10−10760atm V=10−3litre R=0.0821L/K-mol T=293K
Now, PV=nRT n=PVRT n=10−10×10−3760×0.0821×293=5.47×10−18moles ∴ No. of molecules per cm3=5.47×10−18×6.023×1023=3.29×106