Answer:-

To determine whether an element with an atomic number of 90 is diamagnetic or paramagnetic, we need to consider its electron configuration.

The element with an atomic number of 90 is thorium (Th). Its electron configuration can be written as follows:

1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d¹⁰ 4p⁶ 5s² 4d¹⁰ 5p⁶ 6s² 4f¹⁴ 5d¹⁰

Now, to determine its magnetic properties, we need to examine the filling of its electron orbitals. Diamagnetic elements have all of their electron orbitals completely filled with electrons in pairs, which results in all of their magnetic moments canceling out. Paramagnetic elements have unpaired electrons, which result in a net magnetic moment.

In thorium (Th), as shown in the electron configuration above, there are unpaired electrons in the 6s² and 5f¹⁴ orbitals. Since thorium has unpaired electrons, it is paramagnetic.