The central atom/ion of a coordination complex is also referred to as which of the following?

Lewis acid

The correct answer is option 1. Lewis acid.

The central atom or ion of a coordination complex is primarily referred to as a Lewis acid.

Lewis Acid: According to Lewis theory of acids and bases, a Lewis acid is a species that can accept a pair of electrons. In a coordination complex, the central metal ion (or sometimes a metal ion with its associated ligands) acts as a Lewis acid because it accepts electron pairs from the ligands, which act as Lewis bases.

Lewis Base: A Lewis base is a species that can donate a pair of electrons. Ligands in a coordination complex typically act as Lewis bases because they donate electron pairs to the central metal ion.

Bronsted-Lowry Acid: In the context of Bronsted-Lowry theory, an acid is a species that donates a proton (H\(^+\)). This theory focuses on proton transfer reactions, which are not directly applicable to the central metal ion in a coordination complex.

Bronsted-Lowry Base: A base, according to Bronsted-Lowry theory, is a species that accepts a proton (H\(^+\)). Again, this theory is not directly applicable to the central metal ion in a coordination complex.

Therefore, the central atom/ion of a coordination complex is primarily referred to as a Lewis acid because it accepts electron pairs from the ligands (Lewis bases) to form coordinate covalent bonds. The correct answer is: \(\text{Lewis acid}\).