A 1.5 liter flask is filled with nitrogen at a pressure of 12 atmospheres. What size flask would be required to hold this gas at a pressure of 2.0 atmosphere?

Answer 1

P1 V1 = P2 V2

12* 1.5 = 2* V2

that assumes your pressures are abolute. If they are gage pressures then
13 * 1.5 = 3 * V2

Answer 2

1.5 liter flask is filled with nitrogen at pressure of 12 atmosphere. What size would be required to hold this gas at a pressure of 2.0 atmosphere?