Classification of Elements and Periodicity in Properties Previous Year Questions — JEE Main Chemistry
36 past-year Classification of Elements and Periodicity in Properties questions from JEE Main (Chemistry) — page 5.
Q63 (2024)
Element not showing variable oxidation state is:
- Bromine
- Iodine
- Chlorine
- Fluorine
### Core Logic
Fluorine is the most electronegative element and lacks vacant d-orbitals in its valence shell. Consequently, it exhibits only a $-1$ oxidation state (and $0$ in elemental form) and cannot show variable positive oxidation states unlike other halogens.
### Pattern Recognition
First element of a group lacks d-orbitals $\rightarrow$ anomalous properties $\rightarrow$ Fluorine only exhibits $-1$.
### Chapter Mix
Class 11 Chemistry: Classification of Elements and Periodicity in Properties
Q70 (2024)
Given below are two statements:
Statement (I): The 4f and 5f series of elements are placed separately in the Periodic table to preserve the principle of classification.
Statement (II) : S-block elements can be found in pure form in nature.
In the light of the above statements, choose the most appropriate answer from the options given below :
- Statement I is false but Statement II is true
- Both Statement I and Statement II are true
- Statement I is true but Statement II is false
- Both Statement I and Statement II are false
### Core Logic
Statement I is true: The lanthanides ($4\text{f}$) and actinides ($5\text{f}$) are separated at the bottom of the periodic table to avoid distortion of the periodic trends layout and preserve clean structural classification groups.
Statement II is false: s-block elements (alkali and alkaline earth metals) possess exceptionally low ionization energies, making them highly reactive; thus, they are always encountered as compounds rather than in native pure forms in nature.
### Chapter Mix
Class 11 Chemistry: Classification of Elements and Periodicity in Properties
Q61 (2024)
Given below are two statements : one is labelled as Assertion A and the other is labelled as Reason R:
Assertion A: The first ionisation enthalpy decreases across a period.
Reason R: The increasing nuclear charge outweighs the shielding across the period.
In the light of the above statements, choose the most appropriate from the options given below:
- $\text{Both A and R are true and R is the correct explanation of A}$
- $\text{A is true but R is false}$
- $\text{A is false but R is true}$
- $\text{Both A and R are true but R is NOT the correct explanation of A}$
### Core Logic
Assertion A states that the first ionisation enthalpy decreases across a period. This is false, because first ionisation energy generally increases along a period from left to right.
Reason R states that the increasing nuclear charge outweighs the shielding across the period. This is true, and it is the exact reason why the atomic radius decreases and ionisation enthalpy increases across a period.
### Step 1: Final Conclusion
Since the assertion is incorrect and the reason is a factually correct statement, A is false but R is true.
### Pattern Recognition
Recall the horizontal periodic trends: across a period, effective nuclear charge ($Z_{\text{eff}}$) dominates, pulling valence electrons tighter, increasing ionisation energy.
### Evaluation Rubric / Model Answer
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### Chapter Mix
Class 11 Chemistry: Classification of Elements and Periodicity in Properties
Q73 (2024)
Given below are two statements:
Statement I: Along the period, the chemical reactivity of the element gradually increases from group 1 to group 18.
Statement II: The nature of oxides formed by group 1 element is basic while that of group 17 elements is acidic.
In the light above statements, choose the most appropriate from the questions given below:
- $\text{Both statement I and Statement II are true.}$
- $\text{Statement I is true but Statement II is False.}$
- $\text{Statement I is false but Statement II is true.}$
- $\text{Both Statement I and Statement II is false.}$
### Core Logic
Statement I: Along a period, the chemical reactivity of elements first decreases and then increases. Group 1 elements (alkali metals) are highly reactive, Group 17 elements (halogens) are also highly reactive, but the elements in the middle (like carbon) are less reactive. Moreover, Group 18 elements (noble gases) are mostly inert. Therefore, statement I is false.
Statement II: Group 1 elements are metals and form basic oxides (e.g., $Na_2O$). Group 17 elements are non-metals and form acidic oxides (e.g., $Cl_2O_7$). Therefore, statement II is true.
### Pattern Recognition
Reactivity is highest at the extreme left (Group 1) and extreme right (Group 17) of the periodic table, excluding noble gases. Metallic character = basic oxides; Non-metallic character = acidic oxides.
### Evaluation Rubric / Model Answer
null
### Chapter Mix
Class 11 Chemistry: Classification of Elements and Periodicity in Properties
Q84 (2024)
If IUPAC name of an element is "Unununnium" then the element belongs to nth group of periodic table. The value of n is
### Core Logic
Decode the IUPAC name "Unununnium" into its atomic number.
Un = 1
Un = 1
Un = 1
Suffix = ium
So, the atomic number is 111.
### Step 1: Finding group number
For d-block elements with Z > 100, the group number is the last two digits of the atomic number.
Since Z = 111, the element belongs to group 11 (the Copper group).
### Evaluation Rubric / Model Answer
null
### Chapter Mix
Class 11 Chemistry: Classification of Elements and Periodicity in Properties
