  We highlight the main results of a radiative transfer investigation on the
magnetic sensitivity of the solar Mg ii k resonance line at 2795.5 angstrom,
accounting for the joint action of the Hanle and Zeeman effects as well as
partial frequency redistribution (PRD) phenomena. We confirm that at the line
center, the linear polarization signals produced by scattering processes are
measurable, and that they are sensitive, via the Hanle effect, to magnetic
fields with strengths between 5 and 50 G, approximately. We also show that the
Zeeman effect produces conspicuous circular polarization signals, especially
for longitudinal fields stronger than 50 G, which can be used to estimate the
magnetization of the solar chromosphere via the familiar magnetograph formula.
The most novel result is that magneto-optical effects produce, in the wings of
the line, a decrease of the Q/I scattering polarization pattern and the
appearance of U/I signals (i.e., a rotation of the plane of linear
polarization). This sensitivity of the Q/I and U/I wing signals to both weak
(around 5 G) and stronger magnetic fields expands the scientific interest of
the Mg ii k line for probing the chromosphere in quiet and active regions of
the Sun
