91Ó°ÊÓ

The given elements are krypton and Rubidium.

The Stern-Gerlach experiment is based on the demonstration of the spatial orientations of the angular momentum having a dipole moment and having negligible deviations being quantized to get the accurate relation of the changing magnetic field, the dipole, force, and energy relations.

Now, in the Stern-Gerlach experiment, the silver atoms were used due to their property of having less deviation from their incident path, massive mass and having a magnetic dipole moment. Since, the electronic configuration of Silver ($\left[Kr\right]4d^{10}5s^{-1}$) is similar to that of Rubidium ($\left[Kr\right]5s^{-1}$), having one outermost electron, this is more suitable than the element krypton, which is a noble gas.

Also, taking silver atoms was decided because of its neutral electrical properties, which are also satisfied by the element Rubidium.

Hence, the more suitable one is Rubidium.

Again, If Rubidium is also not suitable because its size is smaller than that of silver atoms, causing errors due to major deviations.

Then, the particle with a similar structure to silver atoms, having intrinsic angular momentum as an overall being neutrally electrical particle, would be suitable for conducting this experiment.

Hence, the neutral particles that are stable or long-lived particles are more suitable.