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 6.
Q1940 (2024)
Consider the following elements.
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Which of the following is/are true about $A^\prime$, $B^\prime$, $C^\prime$ and $D^\prime$?
A. Order of atomic radii: $B^\prime < A^\prime < D^\prime < C^\prime$
B. Order of metallic character: $B^\prime < A^\prime < D^\prime < C^\prime$
C. Size of the element: $D^\prime < C^\prime < B^\prime < A^\prime$
D. Order of ionic radii: $B^{\prime +} < A^{\prime +} < D^{\prime +} < C^{\prime +}$
Choose the correct answer from the options given below:
- $\text{ A only}$
- $\text{A, B and D only}$
- $\text{A and B only}$
- $\text{B, C and D only}$
### Core Logic
From the grid layout, $A^\prime$ and $B^\prime$ are in the same period (left to right), while $C^\prime$ and $D^\prime$ are below them in the next period.
In general, moving along a period from left to right, size decreases and metallic character decreases. Moving down a group, size increases and metallic character increases.
Atomic Radii / Size:
$B^\prime < A^\prime$ (across period)
$D^\prime < C^\prime$ (across period)
$A^\prime < C^\prime$ and $B^\prime < D^\prime$ (down the group)
Combining them: $B^\prime < A^\prime < D^\prime < C^\prime$. (Statement A is correct, C is incorrect).
Metallic Character:
$B^\prime < A^\prime$ and $D^\prime < C^\prime$
Overall trend follows size closely for these blocks: $B^\prime < A^\prime < D^\prime < C^\prime$. (Statement B is correct).
Ionic Radii ($+$ ions):
Follows the same basic trend as atomic radii: $B^{\prime +} < A^{\prime +} < D^{\prime +} < C^{\prime +}$. (Statement D is correct).
### Step 1: Final Selection
Statements A, B, and D are correct. Statement C contradicts A, so it is incorrect. Option 2 is the right choice.
### Evaluation Rubric / Model Answer
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### Chapter Mix
Class 11 Chemistry: Classification of Elements and Periodicity in Properties
Q70 (2024)
The correct sequence of electron gain enthalpy of the elements listed below is
A. Ar
B. Br
C. F
D. S
Choose the most appropriate from the options given below:
- $C > B > D > A$
- $A > D > B > C$
- $A > D > C > B$
- $D > C > B > A$
### Core Logic
Electron gain enthalpy ($\Delta_{eg}H$) values are considered with their signs when ordering from largest to smallest algebraically.
<div style="overflow-x: auto; margin: 1rem 0;"><table style="width: 100%; border-collapse: collapse; text-align: left; font-size: 14px;"><thead><tr><th style="border: 1px solid #888; padding: 8px;">Element</th><th style="border: 1px solid #888; padding: 8px;">$\Delta_{eg}H \text{ (kJ/mol)}$</th></tr></thead><tbody><tr><td style="border: 1px solid #888; padding: 8px;">F</td><td style="border: 1px solid #888; padding: 8px;">-333</td></tr><tr><td style="border: 1px solid #888; padding: 8px;">S</td><td style="border: 1px solid #888; padding: 8px;">-200</td></tr><tr><td style="border: 1px solid #888; padding: 8px;">Br</td><td style="border: 1px solid #888; padding: 8px;">-325</td></tr><tr><td style="border: 1px solid #888; padding: 8px;">Ar</td><td style="border: 1px solid #888; padding: 8px;">+96</td></tr></tbody></table></div>
Arranging these algebraically from highest to lowest:
$+96 > -200 > -325 > -333$
Thus, $Ar > S > Br > F$, which corresponds to $A > D > B > C$.
### Pattern Recognition
Noble gases always have positive electron gain enthalpies (highest algebraically). Halogens have highly negative values (lowest algebraically). Fluorine is highly negative, Bromine is slightly less negative. Sulfur sits in between.
### Evaluation Rubric / Model Answer
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### Chapter Mix
Class 11 Chemistry: Classification of Elements and Periodicity in Properties
Q52 (2026)
Which of the following represents the correct trend for the mentioned property?
A. $F > P > S > B$ – First Ionization Energy
B. $Cl > F > S > P$ – Electron Affinity
C. $K > Al > Mg > B$ – Metallic character
D. $K_{2}O > Na_{2}O > MgO > Al_{2}O_{3}$ – Basic character
Choose the correct answer from the option given below.
- $\text{A, B and D only}$
- $\text{A, B, C and D}$
- $\text{A and B only}$
- $\text{B and C only}$
### Core Logic
Analyzing each statement based on periodic trends:
A. On moving left to right in a period, Ionization Energy (IE) generally increases, and from top to bottom it decreases. So, the correct order is $F > P > S > B$ (IE order). Thus, statement A is correct.
B. For Electron Affinity (EA), Group 17 > Group 16 > Group 15. Also, 3rd-period elements often have higher EA than 2nd period (like Cl > F due to compact size of F). The order $Cl > F > S > P$ is correct. Thus, statement B is correct.
C. On moving left to right in a period, metallic character decreases. So $Mg > Al$. The correct order is $K > Mg > Al > B$. Thus, statement C is incorrect.
D. On moving top to bottom in a group basic character increases, and moving left to right it decreases. The correct basic strength order is $K_{2}O > Na_{2}O > MgO > Al_{2}O_{3}$. Thus, statement D is correct.
### Step 1: Conclusion
Statements A, B, and D represent the correct trends.
### Pattern Recognition
Always remember the electron affinity anomaly: $Cl > F$ and $S > O$ due to high inter-electronic repulsion in smaller 2p orbitals.
### Evaluation Rubric / Model Answer
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### Chapter Mix
Class 11 Chemistry: Classification of Elements and Periodicity in Properties
Q60 (2026)
Given below are two statements:
Statement-I: The correct order in terms of atomic/ionic radii is $\text{Al} > \text{Mg} > \text{Mg}^{2+} > \text{Al}^{3+}$.
Statement-II: The correct order in terms of the magnitude of electron gain enthalpy is $\text{Cl} > \text{Br} > \text{S} > \text{O}$.
In the light of the above statements, choose the correct answer from the options given below:
- $(1) \ \text{Both Statement I and Statement II are false}$
- $(2) \ \text{Statement I is false but Statement II is true}$
- $(3) \ \text{Statement I is true but Statement II is false}$
- $(4) \ \text{Both Statement I and Statement II are true}$
### Core Logic
- Statement I: Correct order of size is $\text{Mg} > \text{Al} > \text{Mg}^{2+} > \text{Al}^{3+}$ because atomic radius of magnesium is greater than aluminium in period 3. Thus Statement-I is false.
- Statement-II: Chlorine has the highest electron gain enthalpy in the periodic table, and halogens exceed chalcogens. The order $\text{Cl} > \text{Br} > \text{S} > \text{O}$ is true.
### Step 1: Final Conclusion
Statement I is false but Statement II is true, corresponding to option (2).
### Pattern Recognition
Sees: Periodic trends for atomic radii and electron affinity.
Trap: Assuming Al is larger than Mg due to higher atomic number.
### Chapter Mix
Class 11 Chemistry: Classification of Elements and Periodicity in Properties
Q62 (2026)
Given below are two statements:
Statement-I: $\text{C} < \text{O} < \text{N} < \text{F}$ is the correct order in terms of first ionization enthalpy values.
Statement-II: $\text{S} > \text{Se} > \text{Te} > \text{Po} > \text{O}$ is the correct order in terms of the magnitude of electron gain enthalpy values.
In the light of the above statements, choose the correct answer from the options given below:
- Statement-I is false but Statement-II is true
- Both Statement-I and Statement-II are true.
- Both Statement-I and Statement-II are false.
- Statement-I is true but Statement-II is false.
### Related Formula
$$\text{Half-filled } 2p^3 \text{ configuration of Nitrogen gives higher } IE_1 \text{ than Oxygen (}2p^4\text{).}$$
$$\text{Oxygen has anomalously low magnitude of } \Delta_{eg}H \text{ due to strong inter-electronic repulsions in small } 2p \text{ shell.}$$
### Core Logic
Step 1: Evaluate Statement-I:
- Across Period 2, $IE_1$ generally increases with $Z_{\text{eff}}$.
- N ($2p^3$) is half-filled, so $IE_1(\text{N}) > IE_1(\text{O})$.
- Correct order: $\text{C} < \text{O} < \text{N} < \text{F}$. Statement-I is TRUE.
Step 2: Evaluate Statement-II:
- Magnitudes of $\Delta_{eg}H$ for Group 16: $\text{S} (200) > \text{Se} (195) > \text{Te} (190) > \text{Po} (174) > \text{O} (141\text{ kJ/mol})$.
- Oxygen has the lowest magnitude in the group. Statement-II is TRUE.
### Pattern Recognition
Sees: Group 16 electron gain enthalpy and Period 2 ionization enthalpy anomalies.
Shortcut: Remember half-filled N > O for $IE_1$, and small 2p shell makes O < Po for $|\Delta_{eg}H|$.
### Evaluation Rubric / Model Answer
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### Chapter Mix
Class 11 Chemistry: Classification of Elements and Periodicity in Properties
