Main Group Elements Questions and Answers

Q: Alkali metals form strong complexes with cryptate ligands. The structure of one such crypt given below is of :

It is 2.2.2 crypt ([2.2.2]cryptand).Cryptands are named by the number of oxygen atoms in each of the three bridges joining the two bridgehead nitrogens. Here every bridge is -CH2CH2OCH2CH2OCH2CH2- and holds two oxygens, so the ligand is [2.2.2]. It encloses a metal ion in a three-dimensional cage, which is why its alkali-metal complexes are so stable; its cavity suits K+ best.4.2.2, 6.2.2 and 8.6.2 would need bridges with four, six or eight oxygens, which the drawn ligand does not have.

Q: The set containing all linear polyhalogen compounds is :

The all-linear set is \(\text{I}_{3}^{-}\), \(\text{Cl}_{3}^{-}\), \(\text{BrCl}_{2}^{-}\).Each of these trihalide anions has a central halogen with two bonding pairs and three lone pairs (AX2E3). The three lone pairs occupy the equatorial positions of a trigonal bipyramid, so the two bonded atoms sit on the axis and the ion is linear. ICl2- is linear for the same reason.The trihalogen cations I3+, Cl3+ and BrCl2+ have one electron pair fewer on the central atom: two bonding pairs and two lone pairs (AX2E2), which makes them bent, like water. Every other option contains at least one of these bent cations.

51.

Alkali metals form strong complexes with cryptate ligands. The structure of one such crypt given below is of :

Cryptand: a bicyclic cage in which two bridgehead nitrogen atoms are joined by three identical chains, each -CH2CH2-O-CH2CH2-O-CH2CH2- and so carrying two oxygen atoms

A.4.2.2 crypt
B.6.2.2 crypt
C.2.2.2 crypt
D.8.6.2 crypt

Exam Year(s)

MH SET - 2025, SET Exam - 2025,

Answer: C

It is 2.2.2 crypt ([2.2.2]cryptand).

Cryptands are named by the number of oxygen atoms in each of the three bridges joining the two bridgehead nitrogens. Here every bridge is -CH₂CH₂OCH₂CH₂OCH₂CH₂- and holds two oxygens, so the ligand is [2.2.2]. It encloses a metal ion in a three-dimensional cage, which is why its alkali-metal complexes are so stable; its cavity suits K⁺ best.

4.2.2, 6.2.2 and 8.6.2 would need bridges with four, six or eight oxygens, which the drawn ligand does not have.

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52.

The set containing all linear polyhalogen compounds is :

A.\(\text{I}_{3}^{-}\), \(\text{Cl}_{3}^{-}\), \(\text{BrCl}_{2}^{-}\)
B.\(\text{ICl}_{2}^{-}\), \(\text{I}_{3}^{+}\), \(\text{Cl}_{3}^{+}\)
C.\(\text{I}_{3}^{+}\), \(\text{Cl}_{3}^{+}\), \(\text{BrCl}_{2}^{-}\)
D.\(\text{Cl}_{3}^{-}\), \(\text{BrCl}_{2}^{+}\), \(\text{ICl}_{2}^{-}\)

Exam Year(s)

MH SET - 2025, SET Exam - 2025,

Answer: A

The all-linear set is \(\text{I}_{3}^{-}\), \(\text{Cl}_{3}^{-}\), \(\text{BrCl}_{2}^{-}\).

Each of these trihalide anions has a central halogen with two bonding pairs and three lone pairs (AX₂E₃). The three lone pairs occupy the equatorial positions of a trigonal bipyramid, so the two bonded atoms sit on the axis and the ion is linear. ICl₂^- is linear for the same reason.

The trihalogen cations I₃⁺, Cl₃⁺ and BrCl₂⁺ have one electron pair fewer on the central atom: two bonding pairs and two lone pairs (AX₂E₂), which makes them bent, like water. Every other option contains at least one of these bent cations.

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