Here's how to determine the neutral atom isoelectronic with Rubidium:

1. Understand Isoelectronic:

Isoelectronic species have the same number of electrons.

2. Find Rubidium's Electron Configuration:

Rubidium (Rb) is in Group 1 (alkali metals) and has an atomic number of 37. Its electron configuration is:

[Kr] 5s¹

This means it has 37 electrons.

3. Identify the Neutral Atom with 37 Electrons:

The neutral atom with 37 electrons is Krypton (Kr).

Therefore, Krypton (Kr) is isoelectronic with Rubidium (Rb).