Question

q4. why does earth have the strongest magnetic field among the terrestrial worlds?
it is the only one that has a metallic core.
it rotates much faster than any other terrestrial world.
it is the only one that has both a partially molten metallic core and reasonably rapid rotation.
it is by far the largest terrestrial world.
it is the most volcanically active world.

Explanation:

The generation of a strong magnetic field in a terrestrial planet is related to the dynamo theory. For a planet to have a strong magnetic field, it needs a combination of a partially molten metallic core (to have conductive material in motion) and a reasonably rapid rotation (to drive the convective motion of the molten material). Mercury has a metallic core but its rotation is slow. Venus has a slow rotation. Mars' core is not in a suitable state. Earth has both a partially molten metallic core (outer core is liquid iron - nickel alloy) and a relatively rapid rotation (a day is about 24 hours). The size of the planet (Jupiter is much larger but it's a gas giant, not a terrestrial planet) and volcanic activity are not the key factors for the strength of the magnetic field among terrestrial planets.

Answer:

It is the only one that has both a partially molten metallic core and reasonably rapid rotation.