Unhybridized Orbitals in pi Bonds

[Stuti Pradhan 2J]

From my understanding, there has to be an unhybridized orbital in order for a bond to form. I was wondering if this had to be a unhybridized p orbital or if it could be an unhybridized d orbital as well.

Additionally, in sulfuric acid, H2SO4, the central S atom has an sp3 hybridization. However, since it has an expanded octet, it has two single bonds and two double bonds. Since all the p orbitals are hybridized, do the unhybridized d orbitals play a role in forming the bonds?

Thanks in advance!

[Megan Sparrow 1A]

To answer the first part of your questions, in inorganic chemistry, π bonds can be made from both p- and/or d-orbitals. As long as there is a general overlapping of the electron-dense regions, a pi bond can be formed. The diagram below shows different examples.