We can use the equation of state for an ideal gas to answer the question:

or, by rewriting it,

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.
Explanation:
Below is an attachment containing the solution.
Answer:
the answer is d. 12 protons and no electrons
Explanation:
For Mg atom the atomic number, Z=12
Number of protons in the nucleus = Atomic number of an atom =12