What is na4zi4pang2 (pinyin) in the decomposition of na4 (那)?
There is no  radical, but the left part of 那 can be

冄 rǎn (the same as 冉)
U+5184
Seal Script


That's because in the seal script, 那 is written as


The left part is 冄, and the right part (radical) is 邑. So in 說文解字, it is described as

从邑，冄聲。


But it is better not to call 冄 a &quot;radical&quot;, because modern dictionaries and older dictionaries haven't listed it as a radical.
It is interesting in 康熙字典, 那 has these interchangeable characters:

 

But they are obsolete now, you should not use them.