From the formula of osmotic pressure.
Osmotic Pressure = C * R * T
C= Concentration (under similar condition concentration will remain same)
R = gas constant
T = temperature in kelvin
using formula :
4 = C* R*273 (As O degree C = 273 k) ………(1)
O’ = C * R* 546 ( O’ being the new osmotic pressure) ……………(2)
Dividing 1 and 2 and cross multiplying , we get :
O’ = 8 atm .