the amount of ammonia,
V1 = 450 ml
P1 pressure equals 720 mmHg.
P2 is the standard pressure (1 atm is 760 mmHg).
V2 = the volume,
By applying Boyle's law,
P1V1 =P2V2V2 = P1V1/ P2
= (720 × 450) / 760V2
= 426 ml
426 ml is the volume at standard pressure.
