Ques. 1NEET (UG) 2026
Identify the incorrect statement from the following:
- The largest and the smallest species among Mg, Mg2+, Al and Al3+ are Al and Mg2+, respectively.
- The IUPAC name of the element with atomic number 107 is Unnilseptium.
- The similarity in behaviour of Li with Mg is referred to as 'diagonal relationship'.
- The oxidation state and covalency of Al in [AlCl(H2O)5]2+ are 3 and 6 respectively.
Answer
(1) The largest and the smallest species among Mg, Mg2+, Al and Al3+ are Al and Mg2+, respectively.
Solution
(1) Cations are smaller than their atoms, and across a period size falls: Mg > Al.
Mg2+ and Al3+ are isoelectronic (10 electrons); higher nuclear charge ⇒ smaller ion ⇒ Al3+ < Mg2+.
∴ Size order: Mg > Al > Mg2+ > Al3+ ⇒ largest = Mg, smallest = Al3+. Statement (1) is incorrect.
(2) 1 = un, 0 = nil, 7 = sept ⇒ Unnilseptium (symbol Uns): correct.
(3) As per NCERT, the similarity of Li with Mg (and Be with Al) is called the diagonal relationship: correct.
(4) In [AlCl(H2O)5]2+: x − 1 + 0 = +2 ⇒ x = +3; six ligands are bonded ⇒ covalency 6: correct.
Answer: (1)