We present first a brief overview of an ongoing multi-wavelength
campaign to study the evolution of microflares in active region cores.
The primary new instrument is the Solar X-ray Monitor
(XSM) on board the Chandrayaan-2 mission, which has been providing
since 2019 X-ray spectra with a greater sensitivity than
previous instruments. We then present an analysis of AR12759 as it
crossed the disk in Apr 2020. Using a new Hinode EIS calibration, we
find that the AR core chemical abundances are constant over time,
with the coronal values of Del Zanna (2013). XSM clearly shows
that the abundances of the flare loops are close to photospheric
values, providing new constraints on the chemical fractionation
process. We also present the evolution of the temperature of the
flare loops as obtained from XSM, SDO AIA and Hinode XRT,
and briefly discuss the limitations of current instrumentation
to study the hot (4-12 MK) emission in flares.