Final answer:
Aluminium (Al) is more likely to lose its 3 valence electrons, forming a monatomic ion with a charge of +3 in binary ionic compounds.
Step-by-step explanation:
When atoms form monatomic ions in binary ionic compounds, they do so by either gaining or losing electrons to achieve a stable electron configuration - generally that of a noble gas. Aluminium, symbolized as Al, is in group 13 (or IIIA depending on your system) of the periodic table, having 3 electrons in its outermost shell. To achieve a stable electron configuration, aluminium is more likely to lose these 3 electrons. When Al loses 3 electrons, it forms a monatomic ion with a charge of +3, represented as Al+3. This is because it now has 3 more protons (positive charges) than it does electrons (negative charges).
Learn more about Monatomic ions