Calculations for a bare Nb2C surface predict a 93 Nb CQ of 122 MHz, so the lower observed CQ is also evidence for the surface terminations which result in a more symmetric charge distribution than a bare surface. Basic ordered models for surface-terminated Nb2CTx (Tx = F2, (OH)2, (OH)F, O2, O) give calculated CQ values ranging from 36-109 MHz (Table ), which are consistent with the experimental CQ of 77 MHz. The best agreement is for fluoride and oxide termination, which may suggest a greater proportion of fluoride and oxide terminations than hydroxyl terminations, as previously observed for Ti3C2Tx. Meanwhile, the 93 Nb lineshape of Nb4C3Tx is substantially broader. An exact fitting of the lineshape could not be obtained due to the difficulty of distinguishing a potential distribution of surface terminations, the two Nb sites in Nb4C3Tx, and the NbCx impurity, which all overlap. Nevertheless, based on the linewidth a maximum CQ of ~100 MHz can be determined, ruling out a significant proportion of bare surface (calculated CQ = 135 MHz for the outer Nb2 site, Table ). Given that the calculated quadrupolar parameters for ordered models of surface terminations (Table ) are in the range in the 1 H→ 13 C HETCOR spectrum (Figure ), suggesting that this impurity is predominantly alkyl, while the latter can be observed in a 19 F→ 13 C cross polarization (CP) experiment (Figure ), which, combined with the chemical shift, suggests a -CF2-moiety in a fluorinated organic species. Notably, the C shift increases on etching from the MAX to the MXene for both Nb2CTx and Nb4C3Tx; this is due to an increased Knight shift, corresponding to an increased density of states at the Fermi level for the carbon atoms in the MXene phases. The same increase in C shift was observed for V2CTx (from 208 ppm to 260 ppm), however, in contrast, the C Knight shift actually decreases for Ti3C2Tx (from 566 ppm to 380-410 ppm) .