Answer:
B
Explanation:
To write the electronic configuration of an element using the preceding noble gas configuration, we simply use the noble gas in the previous period of that particular element. We do not use the noble gas of that period in which the element belongs to but the one in the preceding group.
A is wrong
This is because the noble gas in the preceding period is krypton.
In fact, the electronic configuration is [Kr] 4d105s25p3
C is wrong
The noble gas in the last period here is Radon. The electronic configuration of Radium in fact is [Rn] 7s2
D is wrong
The noble gas in the last period before the period of uranium is Radon also. In fact, the electronic configuration of the element is [Rn] 5f36d17s2
B is correct, the actual electronic configuration of the element Cesium is [Xe] 6s1
