Which material is NOT likely to contain lead?

Silica gel is the correct choice because it is a desiccant primarily made from silicon dioxide and is commonly used to absorb moisture. Unlike the other materials listed, which are often associated with lead due to their historical usage or composition, silica gel does not have a known relationship with lead content.

Pipes, especially those installed before the 1980s, frequently contained lead or lead solder, which can leach into water sources. Varnish, particularly older formulations, may have contained lead pigments to enhance color and durability. Shellac, a natural resin used in finishes, sometimes incorporated lead in its production process for similar reasons. Therefore, silica gel stands out as the only material in the choices that is not associated with lead contamination, making it the most accurate answer to the question.