Identify the incorrect statement from the following:

To decide which statement is incorrect we must compare the sizes (ionic/atomic radii) of the four species: Mg (neutral atom), Mg²⁺ (cation), Al (neutral atom) and Al³⁺ (cation).

1. General trend for ionic radii: When an atom loses electrons to form a cation, its radius decreases because the remaining electrons experience a greater effective nuclear charge.

2. Typical radii values (≈ pm):

• Mg (neutral) ≈ 160 pm
• Mg²⁺ ≈ 72 pm
• Al (neutral) ≈ 143 pm
• Al³⁺ ≈ 53 pm

These values are well‑established in standard ionic‑radius tables.

3. Identify the largest species: Among the four, Mg (neutral) has the greatest radius (≈ 160 pm). Al (neutral) is smaller (≈ 143 pm). Both cations are much smaller than their parent atoms.

4. Identify the smallest species: Al³⁺ has the smallest radius (≈ 53 pm), because it has lost three electrons and experiences the strongest effective nuclear charge.

5. Comparison with the statement: The statement claims that the largest species is Al and the smallest is Mg²⁺. According to the data, the actual largest is Mg, and the actual smallest is Al³⁺. Therefore the statement is false.

Hence, the option “The largest and the smallest species among Mg, Mg²⁺, Al and Al³⁺ are Al and Mg²⁺, respectively.” is the incorrect statement.