Identify the incorrect statement from the following :

(A) Atomic radius decreases across a period from left to right, so the atomic radius of Mg is greater than that of Al .
For isoelectronic species, the ionic radius decreases with an increase in nuclear charge. Both \(Mg ^{2+}\) and \(Al ^{3+}\) have 10 electrons, but \(Al ^{3+}\) has a higher nuclear charge \((Z=13)\) compared to \(Mg ^{2+}(Z=12)\), making \(Al ^{3+}\) smaller than \(Mg ^{2+}\).
Cations are always smaller than their respective parent atoms. Therefore, the overall decreasing order of size is \(Mg > Al > Mg ^{2+}> Al ^{3+}\). The largest species is Mg and the smallest is \(Al ^{3+}\). Thus, statement (1) is incorrect.
For atomic number 107, the IUPAC roots are un (1), nil (0), and sept (7), giving the name Unnilseptium. Statement (2) is correct.
Lithium and Magnesium exhibit similar properties due to their comparable polarizing power (charge-to-size ratio), which is known as a diagonal relationship. Statement (3) is correct.
In the complex \(\left[ AlCl \left( H _2 O \right)_5\right]^{2+}\), let the oxidation state of Al be \(x\). We have \(x+(-1)+5(0)=+2 \Rightarrow x=+3\). The central metal atom is surrounded by 6 ligands ( 1 chloride and 5 water molecules), so its covalency is 6 . Statement ( 4 ) is correct.