Final answer:
The atomic number of the element with the noble-gas notation [Kr]5s1 is 36 (b).
Step-by-step explanation:
The atomic number of an element is the number of protons in its nucleus.
The noble-gas notation [Kr]5s1 indicates that the element belongs the atomic number of 36, which is option b.
In this notation, [Kr] represents the electron configuration of krypton (atomic number 36), and 5s1 indicates the presence of one electron in the 5s orbital.