Answer: Volume decreases to half of original volume
Explanation: 
Boyle's Law: This law states that pressure is inversely proportional to the volume of the gas at constant temperature and number of moles.
 (At constant temperature and number of moles)

where,
 = initial pressure of gas = p 
 = final pressure of gas = 2p
 = initial volume of gas = v
 = final volume of gas = ?
Now put all the given values in the above equation, we get the final pressure of gas.


Therefore, the final volume of the gas will become half of initial volume.