What does it mean when chemical A is said to be oxidized?

When a substance is said to be oxidized, it refers specifically to the process of losing electrons. Oxidation is a key concept in redox (reduction-oxidation) reactions, where one species undergoes oxidation while another undergoes reduction, meaning it gains electrons.

The loss of electrons during oxidation typically results in an increase in the oxidation state of the chemical. This is fundamental to understanding how various chemical reactions occur, particularly in biological systems where electron transfer is crucial, such as in cellular respiration and photosynthesis.

In contrast, gaining electrons would describe a reduction process, which is the opposite of oxidation. The idea that a chemical remains unchanged or increases in mass does not capture the essence of oxidation, which specifically refers to alterations in electron configurations and oxidation states.