Which of the following best describes the medium used in lithography?

Lithography is a printing process that relies on the repulsion of oil and water. The medium utilized in lithography is primarily based on greasy substances such as crayon or ink. This technique involves creating an image on a flat surface, typically a stone or metal plate, by applying a grease-based medium. The areas intended to print repel water, while the non-image areas attract it, allowing for the transfer of the greasy medium onto paper during the printing process.

This characteristic of using greasy mediums is what distinguishes lithography from other printing techniques, where different types of inks or paints may be used. In this context, the emphasis on greasy substances is crucial for the lithographic process to function effectively, making it the correct answer.

The other choices reflect various types of inks or mediums but do not accurately capture the essence of what is used in lithography. Water-based and alcohol-based inks belong to different printing technologies that require different methodologies and surfaces, while pigmented pastes typically refer to gouache or other fine art media, which bear no relation to the lithographic process.