directly sampled by the slit (the kernel can also be identified by the saturated region in Figure 1 of Paper I). The kernel was particularly bright between 17:29:48 - 17:31:41 UT; during this time its intensity accounted for 15-20% of the total 2796 Å SJI counts while accounting for only $\sim$1% of the total SJI area. In the following we thus focus on this particular feature, by studying its chromospheric spectra and their evolution, as related to the HXR signatures. Given the high cadence of the HXR data, and the excellent sampling of IRIS, such a dataset is most appropriate to compare with results from hydrodynamical numerical simulations.

Chromospheric dynamics (condensation) {#sec:chrom}
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Aside from the most used Mg [ii]{} h & k doublet, a multitude of chromospheric lines is found within the IRIS spectral range. Together, they can improve the interpretation of line shapes and shifts in terms of physical parameters of the flaring lower atmosphere.

In Paper I we showed the temporal evolution of chromospheric condensation in elementary flare kernels by analyzing the Mg [ii]{} 2791.6Å subordinate line. In particular, we used the position of the line bisector at 30% of the peak intensity level to estimate the 