Answer:
2/3
Explanation:
It is important to bear in mind that momentum is generated by the fluid. Momentum is proportional to the mass and velocity, therefore increasing the mass(density) of the liquid by a factor of 2, while the velocity is constant, increases the momentum of fluid (and rocket) by 2. For any closed system, the momentum is conserved. With that in mind, the momentum of the fluid is equal to but opposite in direction to the momentum of the rocket. Velocity of the rocket given by v=p/m (Where p=momentum of the rocket initially and m is its initial mass). The mass of the rocket increases 3 times. So....
Initially:
vi=p/m
Now:
vf=2p/3m
<h3>The ratio is given by:</h3>
vf:vi = 2p/3m:p/m
I would say the atmosphere.
Hope this helps!