Which branch of chemistry deals with all matter that is now living or was alive at one time?

The correct answer is biochemistry. This branch of chemistry focuses specifically on the chemical processes and substances that occur within living organisms. It encompasses the study of macromolecules such as proteins, nucleic acids, carbohydrates, and lipids, which are vital for life. By understanding these biochemical processes, professionals can gain insights into the functions of cells, metabolism, and the biological mechanisms at play in health and disease.

Organic chemistry, while it does deal with the chemistry of carbon-containing compounds and is foundational in understanding many aspects of biochemistry, is not limited to living or formerly living matter. It also includes synthetic compounds that may not have any biological relevance. Therefore, while organic chemistry is significant, it does not encompass the full scope of the life-related processes that biochemistry addresses.

Inorganic chemistry focuses on inorganic compounds, which include minerals and metals, and does not cover the principles related to living organisms. Physical chemistry, on the other hand, deals with the physical properties and behaviors of chemical systems, so it also does not specialize in the study of living systems. Hence, biochemistry is the most fitting branch when discussing matter that is currently living or was once alive.