Match List I with List II:

Choose the correct answer from the options given below:

The melting point trend in Group 13 is highly irregular.

• Boron (B) has an extremely high melting point because it forms a very strong icosahedral crystalline structure.
• Gallium (Ga) has an unusually low melting point (about 303 K) because it exists as Ga2 molecules in the crystal lattice rather than a standard metallic structure.
• The Trend: B > Al > Tl > In > Ga

Unlike atomic radii, the ionic radii of M+3 ions follow a regular trend. As you move down the group, more shells are added, and the effective nuclear charge felt by the outermost electrons (in an ionic state) allows for a consistent increase in size.

• The Trend: Tl > In > Ga > Al > B.
  

The First Ionization Enthalpy is irregular due to poor shielding by d and f electrons.

• Boron is highest due to its small size.
• Thallium (Tl) is higher than Aluminium and Gallium due to the Lanthanoid Contraction (poor shielding by 4f electrons), which makes the nucleus hold the 6s2 electrons very tightly.
• Gallium is slightly higher than Aluminium due to the d-block contraction.
• The Trend: B > Tl > Ga > Al > In

Normally, atomic radius increases down a group. However, there is a anomaly between Aluminium and Gallium.

• Gallium vs. Aluminium: Gallium follows the 10 elements of the first transition series 3d10. The 3d electrons shield the nuclear charge poorly, causing the outer electrons to be pulled in more strongly. Consequently, the atomic radius of Gallium is slightly smaller than (or nearly equal to) Aluminium.
• The Trend: Tl > In > Al > Ga > B.