Your gas contains
The first important thing to notice is that the gas is tetra-atomic,
So, if you know how many molecules you have, you can determine how many atoms are present by multiplying that number by 4.
In order to get the number of molecules, you need the number of moles of gas first. Notice that the temperature of the gas is
These are actually the old conditions given for STP, which implies that 1 mole of your gas will occupy exactly 22.4 L - this is known as the molar volume of gas at STP.
SInce you're dealing with a volume of 1.4 L, the number of moles of gas present is
To get the number of molecules present in this many moles, use the fact that 1 mole of a substance contains exactly
Finally, get the number of atoms by multiplying this number by 4
I'll leave the answer rounded to two sig figs