# Q.29. The pressure of interstellar space is about 4.0$×{10}^{-22}$ atm. If the temperature is 3 K, how many molecules are present per litre? (R = 0.08 l-atm/K-mol) (a) 2430 (b) 1420 (c) 845 (d) 1002

Dear Student,

According to the gas law:

P = 4 x 10-22 atm.
T = 3 K
V is to considered as unity as no. of molecules is to be calculated per unit volume.
Putting these values:

As 1 mol = 6 x 1023  molecules.
so,
50/3 x 10-22 mol will contain = 6 x 1023 x 50/3 x 10-22 molecules
=  100.2 x 10
= 1002 molecules

So, 1002 molecules are present per unit volume of the interstellar space.
So, the option ( d ) is correct .

Regards.

• -2
Use pv= nrt
• -1
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