The section presents a question related to atomic structure and ion formation. It asks what type of ion an atom becomes when it loses an electron. The options provided are:

A. Ion dương (Positive ion)
B. Ion âm (Negative ion)
C. Nguyên tử trung hòa (Neutral atom)
D. Không xác định (Undefined)

Key topics include ionization, electron loss, and the resulting charge of an atom. The main entity is the atom and its transformation into an ion.