Answer : The number of molecules of gas in a sample are 
Explanation :
First we have to calculate the moles of carbon dioxide gas in a sample.

where,
P = pressure of carbon dioxide gas = 0.955 atm
V = volume of carbon dioxide gas = 500.0 mL = 0.500 L
T = temperature of carbon dioxide gas = 
n = number of moles of carbon dioxide gas = ?
R = gas constant = 0.0821 L.atm/mol.K
Now put all the given values in the ideal gas equation, we get:


Now we have to calculate the number of molecules of gas in a sample.
As we know that, 1 mole of gas contains
number of molecules of gas.
As, 1 mole of carbon dioxide gas contains
number of molecules of gas.
So, 0.0201 mole of carbon dioxide gas contains
number of molecules of gas.
Therefore, the number of molecules of gas in a sample are 