4$f$- orbitals more diffused than the 5$f$-orbitals

Lesser energy difference between 5$f$ and 6$d$ than between 4$f$ and 5$d$-orbitals

More energy difference between 5$f$ and 6$d$ than between 4$f$ and 5$d$-orbitals.

More reactive nature of the actinoides than the lanthanoides

Soft and can be cut with a knife

Low ionization energy

High electronegativity

Form ionic compounds

$f$-block

$d$-block

High atomic masses

Radioactive series

Actinium (Ac)

Thorium (Th)

Uranium (U)

Protactinium (Pa)

High ionization energy of 4f electrons

Low electronegativity of gadolinium

Shielding by 5s and 5p orbitals

Relativistic effects on 4f orbitals

[Xe] 4f⁸ 6s¹

[Xe] 4f⁷ 6s²

[Xe] 4f⁶ 6s² 6p¹

[Xe] 4f⁶ 5d¹ 6s²

Are generally soft.

Have shiny surfaces when freshly cut.

Exhibit characteristic flame colors.

Produce a violet flame when heated.

Larger ionic radii

Greater nuclear charge

Presence of f-orbitals

Small energy difference between 5f, 6d, and 7s orbitals

Variable oxidation state, usually +3

Strong oxidizing agents

Radioactive nature in all isotopes

Formation of covalent compounds primarily

All lanthanides have similar densities

The most common oxidation state of lanthanides is +3

All lanthanides are paramagnetic

Lanthanides show a variety of colors in their solid-state and solutions

Overlapping of inner orbitals

Free movement of electrons over all the orbitals

Small energy difference between $5f$ and $6d$ levels

None of the above