The magnetosphere of jupiter is
a. a region of charged particles extending along the orbit of the satellite io, forming a ring around jupiter.
b. a dark belt around the planet's equator where intense electric currents flow, generating the planet's magnetic field.
c. the magnetized hydrogen in the inner regions of jupiter just outside the solid core, where the planet's magnetic field is produced.
d. a large region outside jupiter occupied by its magnetic field and filled with high-energy charged particles.

d. a large region outside Jupiter occupied by its magnetic field and filled with high-energy charged particles.  

Explanation:

A magnetic field is generated by the movement of a charged particle in the space around it. For the case of Jupiter its magnetic field is created by the liquid metallic hydrogen in its core.

So the magnetosphere is just the magnetic field around a planet, which interacts with high-energy charged particles (for example: Cosmic Rays).

Magnetospheres protect planets from the extreme radiation coming from stars or another interstellar source.