Orthoboric acid (H₃BO₃) is a weak inorganic acid with unique properties. Let's analyze each statement:

Statement 1: "Acidity of its aqueous solution increases upon addition of ethylene glycol"

This is correct. Orthoboric acid acts as a Lewis acid rather than a typical Brønsted acid. It accepts OH^- ions:

Ethylene glycol (HO-CH₂-CH₂-OH) forms a stable chelate complex with boric acid, enhancing its acidity by stabilizing the borate anion through chelation effect.

Statement 2: "It has a three dimensional structure due to hydrogen bonding"

This is incorrect. Orthoboric acid forms a layered two-dimensional structure through hydrogen bonding, not three-dimensional. The molecules are arranged in planar sheets with hydrogen bonds within each layer, but weak van der Waals forces between layers.

Statement 3: "It behaves as a weak acid in water due to self ionization"

This is incorrect. Boric acid behaves as a weak acid not due to self-ionization but because it acts as a Lewis acid that accepts hydroxide ions from water (as shown above), not by donating protons like typical acids.

Statement 4: "It is a weak electrolyte in water"

This is correct. Since boric acid only partially dissociates in water (K_a ≈ 5.8 × 10^-10), it conducts electricity poorly, making it a weak electrolyte.

Summary of Correct Statements:

Only statements 1 and 4 are correct.

Related Concepts:

Lewis Acids: Substances that accept electron pairs. Boric acid is a classic example of a Lewis acid rather than a Brønsted acid.

Hydrogen Bonding: The intermolecular force responsible for boric acid's layered crystal structure.

Weak Electrolytes: Compounds that partially dissociate in solution, resulting in low electrical conductivity.

Key Formulae:

Acid dissociation constant for boric acid: K_a = 5.8 × 10^-10

Reaction with polyhydroxy compounds: Enhanced acidity through chelate formation