Which one of the following was not present during the Mesozoic Era of the geological time scale ?

The correct option is Bryophytes.

To understand why Bryophytes is the correct answer, let us look at the evolutionary timeline of plants in relation to the geological time scale.
The geological time scale is divided into several eras, including the Paleozoic, Mesozoic, and Cenozoic eras. The Mesozoic Era (often called the "Age of Reptiles" or "Age of Conifers") spanned from about 252 to 66 million years ago.

Bryophytes (which include liverworts, hornworts, and mosses) are among the earliest land plants. Fossil evidence and evolutionary studies show that bryophytes diverged and were already well-established during the early Paleozoic Era, specifically around the Ordovician Period (roughly 470 million years ago). Therefore, they did not originate or first appear in the Mesozoic Era; they predate it by hundreds of millions of years.
In contrast, plants like ferns, horsetails, and ginkgos experienced significant evolutionary developments, radiations, or dominance during the Mesozoic Era. Ginkgos, for instance, reached their peak diversity and distribution during this era.