The group of molecules that form a life code in the nucleus of cells are nucleic acids, specifically DNA (deoxyribonucleic acid).

Here's why:

* DNA contains genetic instructions: DNA is made up of nucleotides, which are arranged in a specific sequence that acts as a blueprint for building and maintaining an organism.

* DNA is located in the nucleus: The nucleus is the control center of the cell, and it houses the cell's DNA.

* DNA is transcribed into RNA: DNA's instructions are copied into RNA (ribonucleic acid), which then directs protein synthesis. Proteins are the workhorses of the cell, carrying out a vast array of functions.

While RNA is also a nucleic acid and plays a crucial role in protein synthesis, it is DNA that holds the primary genetic code and is responsible for passing on hereditary information from one generation to the next.