So this molecule is, in fact, resonant stabilized. And finally, let's look at histidine. Now, we saw that Lysine and Arginine are always positively charged at the physiological PH of around seven. The thing about histidine is, even though it is basic, it bears a full positive charge on that side chain group. It can also sometimes be neutral at the physiological PH of around seven. That's because, unlike in this case, in this case, the PKA value here is around six.