Periodic Table

Step 1: Recall the structure of the periodic table.

The number of elements in a period depends on the subshells being filled:

• Period 1: → 2 elements,
• Period 2: → 8 elements,
• Period 3: → 8 elements,
• Period 4: → 18 elements.

Step 2: Identify the number of elements in the 4th period.

In the 4th period, the , , and subshells are filled. These subshells accommodate a total of:

Final Answer: The number of elements in the 4th period is , which corresponds to option .

Correct answer: Ar

Explanation:
Argon (Ar) is a chemical element that belongs to Group 18 of the modern periodic table, also known as the noble gases. These elements are characterized by their full outer electron shells, making them chemically inert or unreactive.

On the other hand:
- (Fluorine),
- (Chlorine), and
- (Iodine)
are all halogens (Group 17 elements), and they are not noble gases.

Correct answer: 8

Explanation:
The 3rd period of the modern periodic table contains 8 elements. These elements are from s-block and p-block, with the electron filling in the 3s and 3p orbitals.

The elements in the 3rd period are:
Sodium (Na), Magnesium (Mg), Aluminium (Al), Silicon (Si), Phosphorus (P), Sulfur (S), Chlorine (Cl), and Argon (Ar)

So, the number of elements in the 3rd period is 8.

Correct answer: f-block elements

Explanation:
Lanthanoids are a series of elements from atomic number 57 (Lanthanum) to 71 (Lutetium). These elements are placed in the f-block of the modern periodic table and are characterized by the filling of the 4f orbitals.

- s-block elements: Include Group 1 and Group 2 elements.
- p-block elements: Include Groups 13 to 18.
- d-block elements: Are the transition metals, found in Groups 3 to 12.
- f-block elements: Include lanthanoids and actinoids.
Therefore, lanthanoids belong to the f-block elements.

Correct answer: Principal quantum number

Explanation:
In the Modern Periodic Table, as we move down a group, new electron shells are added to the atoms of the elements. This means the value of the principal quantum number (n) increases.

- Principal quantum number (n): Represents the main energy level or shell. It increases with each period down the group.
- Azimuthal quantum number (l): Depends on the value of and can vary within the same shell.
- Magnetic quantum number (m): Depends on , and does not follow a regular trend down the group.
- Spin quantum number (s): Always or , so it remains constant.
Thus, the quantum number that increases down the group is the Principal quantum number.

The elements in Group VII A of the periodic table are known as halogens. This group includes fluorine (F), chlorine (Cl), bromine (Br), iodine (I), and astatine (At). They are highly reactive nonmetals and are characterized by having seven valence electrons. Thus, the family name of VII A group elements is halogens.

The correct option is (D) : Halogens

Dobereiner's law of triads : This classification is based on the atomic weights of elements. Dobereiner grouped elements into triads where the atomic weight of the middle element was approximately the average of the other two.

Newlands' law of octaves : This also used atomic weights, classifying elements into groups of eight, similar to the octaves in music, where every eighth element had similar properties.

Mendeleev's periodic table: Mendeleev’s periodic table was originally based on atomic weights and he arranged elements in order of increasing atomic weight, recognizing that elements with similar properties occurred at regular intervals.

Modern periodic table : The modern periodic table is based on the atomic number (number of protons), not atomic weight. This is a key difference from the older classifications.

The correct option is (D): Modern periodic table

Propyne is an alkyne with the molecular formula . It contains a triple bond between two carbon atoms.
The correct structure is:

- It has three carbon atoms in a chain.
- A triple bond exists between the second and third carbon atoms.
- The first carbon is part of a methyl group ( ).
Therefore, the correct structure of propyne is .

The periodic table is arranged such that elements in the same group have the same number of valence electrons. The group number generally indicates the number of valence electrons for elements in groups 1, 2, and 13-18. Element X belongs to the 2nd group and 3rd period.

Elements in the 2nd group are called alkaline earth metals and have 2 valence electrons. The valency of an element is determined by the number of electrons it can gain, lose, or share to achieve a stable electron configuration (usually a noble gas configuration).

Since element X has 2 valence electrons, it tends to lose these 2 electrons to achieve a stable configuration.

Therefore, its valency is 2. So, the correct answer is (2) 2.

Final Answer: The final answer is

The elements of Group IV A (also known as Group 14) are carbon (C), silicon (Si), germanium (Ge), tin (Sn), and lead (Pb). These elements are called the carbon family.

The chalcogen family (Group 16) includes oxygen, sulfur, selenium, tellurium, and polonium.
The nitrogen family (Group 15) includes nitrogen, phosphorus, arsenic, antimony, and bismuth.
The boron family (Group 13) includes boron, aluminum, gallium, indium, and thallium.