Question

Which elements are placed at the bottom of the periodic table?

• A. Lanthanides
• B. Halogens
• C. Inert gases
• D. Alkali metals

Answer 1

The correct option is A

Lanthanides

The explanation for the correct option:

(A) Lanthanides :

• The lanthanide sequence contains elements 58 to 71 that fill their 4f sub-level.
• They are referred to as lanthanides because the lanthanum element (atomic number 57), the first in the group,
• The properties of lanthanides and actinides resemble each other very closely but are different from the rest elements due to the preferential filling of f-orbitals.
• These have been placed separately at the bottom of the periodic table for convenience and to avoid unnecessary sidewise expansion of the periodic table so the structure of the periodic table is maintained.

The explanation for the incorrect options:

(B) Halogens:

• They occupy the seventh group of the periodic table.
• They are highly electronegative non-metals their valance shell has a vacancy of one electron.
• The halogens are Fluorine (F), Chlorine (Cl), Bromine (Br), Iodine (I), and Astatine (At).

(C) Inert Gas:

• They occupy the eighteenth group of the periodic table.
• They are non-reactive gases as their valance shell is completely filled.
• The noble gases or inert gases are Helium (He), Neon (Ne), Argon (Ar), Krypton (Kr), Xenon (Xe), and Radon (Rn).

(D) Alkali metals:

• They occupy the first group of the periodic table.
• The s-block elements having only one electron in their s-orbital are called group one or alkali metals.
• The alkali metals consist of the chemical elements: Lithium (Li), Sodium (Na), Potassium (K), Rubidium (Rb), Cesium (Cs), and Francium (Fr).

Thus, option (A) Lanthanides is a correct answer as they are placed at bottom of the periodic table.