We can use the equation of state for an ideal gas to answer the question:
[tex]pV=nRT[/tex]
or, by rewriting it,
[tex]p= \frac{nRT}{V} [/tex]
where p is the gas pressure, V its volume, T its temperature, n the number of moles of the gas and R the gas constant.
When the gas is sprayed from the can into the room, its volume V has increased, while n (the number of moles of the gas) stayed the same. Since R is a constant and the temperature T also stayed constant, if we look at the formula we see that the numerator didn't change, while the denominator (V) has increased, so the pressure of the gas has decreased.
