Which of earth's parameters would be affected by a change in its rotational speed?
a.
temperature
b.
pressure
c.
density
d.
size

The C. density would be affected by a change in the rotational speed of the Earth.  

If the Earth spins faster, the gravity will become denser and if it spins slower than usual, the gravitational pull will be weak.

The rotation speed of the Earth is about 1670 km per hour. The spherical shape of the earth is the result of its rotational speed. If the Earth rotates faster, there will be destruction everywhere. Sea levels will rise in an unimaginable way, the atmosphere will evade from Earth, the gravitational field will be way stronger, etc.