Periodic Table

To solve the problem, we need to understand what the 4f elements are called.

1. The 4f Elements:
The 4f elements are elements whose electrons fill the 4f orbital. These elements belong to the lanthanide series and are also known as lanthanoids.

2. Conclusion:
The 4f elements are called Lanthanoids.

Final Answer:
The 4f elements are called .

To determine the block to which elements with atomic numbers , , , and belong, we need to analyze their electron configurations and placement in the periodic table.

1. Understanding Atomic Numbers and Electron Configurations:
The atomic number of an element corresponds to the number of protons in its nucleus, which also determines its electron configuration. Elements are classified into blocks (s, p, d, f) based on the subshell in which their outermost electrons reside.

2. Analyzing Each Element:

- Element with Atomic Number 3 (Lithium, Li):
The electron configuration of lithium is . The outermost electron is in the subshell.
Element with Atomic Number 11 (Sodium, Na):
The electron configuration of sodium is . The outermost electron is in the subshell.
Element with Atomic Number 19 (Potassium, K):
The electron configuration of potassium is . The outermost electron is in the subshell.
Element with Atomic Number 37 (Rubidium, Rb):
The electron configuration of rubidium is . The outermost electron is in the subshell.

3. Identifying the Block:
All these elements ( , , , ) have their outermost electrons in the subshell. Therefore, they belong to the block of the periodic table.

4. Conclusion:
Elements with atomic numbers , , , and belong to the block.

Final Answer:

To solve the problem, we need to understand the historical context of the discovery of elements and the concept of "eka-elements."

1. Understanding Eka-Elements:
The term "eka-element" was used by chemists in the 19th century to predict the existence of undiscovered elements based on their expected properties and positions in the periodic table. The prefix "eka-" (meaning "one" in Sanskrit) was used to denote an element that would occupy a position one place below a known element.

2. Eka-Aluminium:
Eka-Aluminium refers to the element predicted to be located directly below aluminum ( ) in the periodic table. According to Mendeleev's periodic table, which was developed in the late 19th century, the element below aluminum should have similar chemical properties but with increased atomic mass.

3. Discovery of Gallium:
In 1875, the French chemist Paul Émile Lecoq de Boisbaudran discovered the element gallium ( ). Gallium was found to fit perfectly into the position predicted for Eka-Aluminium in Mendeleev's periodic table. It has similar chemical properties to aluminum, such as being a soft metal with a low melting point, and it occupies the same group (Group 13) as aluminum.

4. Analyzing the Options:
- (1) Scandium: Incorrect. Scandium is a transition metal and does not belong to Group 13.
- (2) Gallium: Correct. Gallium was discovered in the place of Eka-Aluminium and fits the predicted properties.
- (3) Germanium: Incorrect. Germanium is a metalloid and belongs to Group 14, not Group 13.
- (4) Boron: Incorrect. Boron is a nonmetal and belongs to Group 13 but is above aluminum, not below it.

5. Conclusion:
The element discovered in the place of Eka-Aluminium is gallium ( ).

Final Answer:

To solve the problem, we need to understand the historical context of the discovery of elements and the concept of "eka-elements."

1. Understanding Eka-Elements:
The term "eka-element" was used by chemists in the 19th century to predict the existence of undiscovered elements based on their expected properties and positions in the periodic table. The prefix "eka-" (meaning "one" in Sanskrit) was used to denote an element that would occupy a position one place below a known element.

2. Eka-Aluminium:
Eka-Aluminium refers to the element predicted to be located directly below aluminum ( ) in the periodic table. According to Mendeleev's periodic table, which was developed in the late 19th century, the element below aluminum should have similar chemical properties but with increased atomic mass.

3. Discovery of Gallium:
In 1875, the French chemist Paul Émile Lecoq de Boisbaudran discovered the element gallium ( ). Gallium was found to fit perfectly into the position predicted for Eka-Aluminium in Mendeleev's periodic table. It has similar chemical properties to aluminum, such as being a soft metal with a low melting point, and it occupies the same group (Group 13) as aluminum.

4. Analyzing the Options:
- (1) Scandium: Incorrect. Scandium is a transition metal and does not belong to Group 13.
- (2) Gallium: Correct. Gallium was discovered in the place of Eka-Aluminium and fits the predicted properties.
- (3) Germanium: Incorrect. Germanium is a metalloid and belongs to Group 14, not Group 13.
- (4) Boron: Incorrect. Boron is a nonmetal and belongs to Group 13 but is above aluminum, not below it.

5. Conclusion:
The element discovered in the place of Eka-Aluminium is gallium ( ).

Final Answer: