What is the impulse of a 25 N force exerted over 0.5 seconds?

Actually Welcome to the Concept of the Impulse.

Impulse is denoted by 'J'

hence, J = F. dt

so we get as,

J = (25)*(0.5)

J = 750 N-s

===> hence the impulse is 12.5 N-s

answer;

d. are made mostly of liquid

explanation;

-the general   composition and structure planets includes; they have a thick gas and liquid layer covering a small,solid core. mostly the gases are hydrogen and helium atmosphere and layers of liquid hydrogen. for instance neptune and uranus are examples of the outer planets, they have a core covered by ice and ammonia.

-neptune's atmosphere is hydrogen and helium with a bit of methane so there is no oxygen to breath and the interior is made up of frozen water and ammonia with a rock and iron core. thus, there is no liquid water or solid surface to survive.