Gases at constant temperature follow Boyle’s law, where it states that pressure is inversely proportional to gases at constant temperature. 
PV = k where P pressure, V - volume and k - constant 
At 2 instances 
P1V1 = P2V2
Where the 1st instance parameters are on the left side and 2nd instance parameters on the right side 
1.20 uL x 500 kPa = V2 x 101.3 kPa
V2 = 1.20 x 500 / 101.3
 The volume when pressure is dropped is 5.92 uL