Answer
See a detailed answer below,
Work Step by Step
To answer this question, let's have a look at the water phase diagram in Figure 16.4 in your textbook.
We know that under the water surface by 100 m, the pressure is higher than the pressure at the surface.
$$P=P_a+h\rho g=(1.013\times 10^5)+(100)(1030)(9.8)$$
$$P=1.11\times 10^6\;\rm Pa\approx \bf 11 \;\rm Pa=11\;atm$$
So, in the water phase diagram, we can see that at higher pressures the freezing point goes below zero.
This means that the freezing point will be lower than the freezing point at the surface.
And at the same time, we can see that the boiling point moves up when the pressure goes up.
This means that the boiling point will be higher than the boiling point at the surface.
