At 25oc, three moles of a gas occupy a volume of 4.0 l at 1.9 kpa. if the volume increases to 12.0 l, what will the new pressure be?
a. 5.70 kpa
b. 0.63 kpa
c. 1.0 kpa
d. 3.3 kpa

The
according to Boyle's law concerning Pressure (P), Volume (V), Temperature (T) and number of mole (n) , we have the famous formula:

PiVi = Pf Vf, 

Pi=1.9kPa
Vi= 4L
Vf = 12L
T=25
n=3 
Pf = ?
let's find the value of Pf
from the equation
PiVi   = Pf Vf  we can have Pf= PiVi  / Vf

Pf = 1.9*4 / 12 = 0.63

so the answer is B. 0.63 kPa