Which location in the cell is unlikely to contain ribosomes and ribosomal subunits?

The correct answer is Smooth Endoplasmic reticulum.

Ribosomes are distinct from other organelles as they possess no membrane enveloping them, which differs from other organelles, they comprise of two subunits, and when they are generating some of the proteins they can turn membrane bound to the ER.

The smooth endoplasmic reticulum does not possess ribosomes on its surface and thus does not take part in the formation of proteins. The SER has been found to take part in the synthesis of steroids.