Periodic Table Previous Year Questions with Solutions

1.0Classification of Elements and Periodicity in Properties

The Periodic Table is an organized arrangement of elements based on their atomic number, electron configuration, and recurring chemical properties. Initially proposed by Dmitri Mendeleev, it has been refined over time to align with modern atomic theory.       

The periodic table is a systematic arrangement of elements, grouping those with similar properties together.

2.0Key Concepts to Remember 

Groups in the Periodic Table

The periodic table consists of 18 vertical columns known as groups. Elements in the same group form a family and are often named after the first element in the group. Some groups also have specific names, including:

1. Group 1 – Alkali Metals
2. Group 2 – Alkaline Earth Metals
3. Group 15 – Pnicogens
4. Group 16 – Chalcogens
5. Group 17 – Halogens
6. Group 18 – Noble Gases (or Aerogens)

All other groups are generally named after their first element.

Periods in the Periodic Table

The horizontal rows in the periodic table are called periods. There are seven periods in the long-form periodic table:

1. 1st period (H → He) contains only 2 elements, making it the shortest period.
2. 2nd period (Li → Ne) and 3rd period (Na → Ar) contain 8 elements each and are referred to as short periods.
3. 4th period (K → Kr) and 5th period (Rb → Xe) contain 18 elements each and are considered long periods.
4. 6th period (Cs → Ra) is the longest period, with 32 elements.
5. 7th period starts with Fr (Francium) and remains incomplete, containing 19 elements so far.

Shielding Effect (Screening Effect)

In multi-electron atoms, the outermost (valence) electrons experience both:

• Attraction from the positively charged nucleus.
• Repulsion from inner-shell electrons.

This reduces the effective nuclear attraction on valence electrons, a phenomenon called the shielding or screening effect.

Effective Nuclear Charge (Z_eff)

The effective nuclear charge  (Z_eff) is the net positive charge experienced by an electron. It is calculated using the formula:

Z_eff = Z − 𝛔

Where:

• Z = Actual nuclear charge
• 𝛔 = Screening constant

Across a period (left to right), the effective nuclear charge increases, due to greater nuclear attraction.

3.0Periodic Trends in Properties

Ionization Energy

• Definition: The energy required to remove an electron from an atom.
• Trend in a Group: Decreases down a group as atomic size increases.
• Trend in a Period: Increases across a period due to stronger nuclear attraction.

Electron Affinity

• The energy released when an electron is added to a neutral gaseous atom.

Electronegativity

• Definition: The tendency of an atom to attract a bonded pair of electrons.
• Trend in a Period: Increases from left to right due to decreasing atomic size and increasing nuclear charge.
  Alkali metals have the lowest electronegativity.
  Halogens have the highest electronegativity.
  Noble gases have zero electronegativity.
• Trend in a Group: Decreases from top to bottom due to increasing atomic size.

Electronegativity Scales

1. Mulliken’s Scale: Defines electronegativity as the average of ionization potential and electron affinity. 

Electronegativity=  Ionization Potential+Electron Affinity2
Pauling’s Scale: The most commonly used scale, based on bond energy differences.
ΔE=(Actual Bond Energy)−(E_A−A  * E_B−B)

The relationship between Pauling and Mulliken electronegativity values is:
𝜒(Pauling) = 0.34×𝜒(Mulliken) − 0.2

4.0Other Periodic Properties

Atomic Volume

• The volume occupied by one gram-atom of an element.
• Calculated as:
  Atomic Volume=Gram Atomic Weight/Density (in solid state)
• Measured in c.c./mole.

Density

• Varies periodically with atomic number.
• Generally, increases within a period, reaching a maximum at central elements, then decreases.

Melting and Boiling Points

• Exhibit periodic trends across the periodic table.
• Generally, increase across a period and decrease down a group.

Oxidation State (Oxidation Number, O.N.)

• Indicates the total number of electrons gained or lost by an atom when forming a compound.

Magnetic Properties

• Depends on the electronic structure of individual atoms.

5.0JEE Main Past Year Questions with Solutions on Periodic Table

Q.1  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 :

(1) Statement I is false but Statement II is true

(2) Both Statement I and Statement II are true

(3) Statement I is true but Statement II is false

(4) Both Statement I and Statement II are false

Ans.   (3)

Sol. s-block elements are highly reactive and found in combined state.

Q.2  The correct order of first ionization enthalpy values of the following elements is :

(A) O                                  

(B) N

(C) Be                                

(D) F

(E) B

Choose the correct answer from the options given below :

(1) B < D < C < E < A     (2) E < C < A < B < D

(3) C < E < A < B < D    (4) A < B < D < C < E

Ans.   (2)

Sol. Correct order of I^st IE

Li < B < Be < C < O < N < F < Ne

↓    ↓              ↓    ↓     ↓               

E < C  <  A < B < D

Q.3  The transition metal having highest 3^rd ionisation enthalpy is :

(1) Cr                   

(2) Mn                  

(3) V                       

(4) Fe

Ans.   (2)

Sol. 3rd Ionisation energy : [NCERT Data]

V : 2833 KJ/mol

Cr : 2990 KJ/mol    Mn : 3260 KJ/mol              Fe : 2962 KJ/mol

Alternative

Mn : 3d⁵ 4s² Fe : 3d⁶ 4s² Cr : 3d⁵ 4s¹      V : 3d³ 4s²

So Mn has the highest 3rd IE among all the given elements due to d⁵ configuration.

Q.4 Given below are two statements :

Statement (I) : Both metal and non-metal exist in p and d-block elements.

Statement (II) : Non-metals have higher ionisation enthalpy and higher electronegativity than the metals.

In the light of the above statements, choose the most appropriate answer from the option given below:

(1) Both Statement I and Statement II are false

(2) Statement I is false but Statement II is true

(3) Statement I is true but Statement II is false

(4) Both Statement I and Statement II are true

[2024]

Ans. (2)

Sol.   I. In p-Block both metals and non metals are present but in d-Block only metals are present.

II.  EN and IE of non metals are greater than that of metals      

I - False, II-True

Q.5 It is observed that characteristic X-ray spectra of elements show regularity. When frequency to the power 'n' i.e. vⁿ of X-rays emitted is plotted against atomic number 'Z', the following graph is obtained.                                                                                                                            

The value of 'n' is

(1) 1                          

(2) 2                 

(3) 12              

(4) 3

Ans.  (3)

Sol.   According to Henry Moseley √v     ∝  z  – b  

So n =   12 

Q.6 For electron gain enthalpies of the elements denoted as D_egH, the incorrect option is :

(1) Δ_egH (Cl) < Δ_egH (F)

(2) Δ_egH (Se) < Δ_egH (S)

(3) Δ_egH (I) <  Δ_egH (At)

(4) Δ_egH (Te) < Δ_egH (Po)                                                   

Ans. (2)

Sol.       

(1)  Δ_egH (Cl) <  Δ_eg H (F)

(–345)  (– 328) Correct                         

(2) Δ_egH (Se) <  Δ_egH (S)

(–195)  (– 200) Incorrect                       

(3)  Δ_eggH (I) <  Δ_egH (At)

(–295) (– 270) Correct                          

(4)  Δ_egH (Te) <  Δ_egH (Po)

(–190)  (– 183) Correct

Q.7 Given below are two statements: one is labelled as Assertion A and the other is labelled as Reason R

Assertion A: 5f electrons can participate in bonding to a far greater extent than 4f electrons

Reason R: 5f orbitals are not as buried as 4f orbitals

In the light of the above statements, choose the correct answer from the options given below

(1)   Both A and R are true but R is NOT the correct explanation of A

(2)   Both A and R are true and R is the correct explanation of A

(3)   A is false but R is true

(4)   A is true but R is false       

[2023]

Ans. (2)

Sol. 5f orbital not buried as 4f orbitals so e^– present in 5f orbital experience less nuclear attraction than e^– present in 4f orbital. Hence electrons of 5f orbital can take part in bonding to a far greater extent. 

Q.8 Outermost electronic configurations of four elements A, B, C, D are given below:

1. 3s²         (B)   3s²3p¹        (C)   3s²3p³   (D)   3s²3p⁴

The correct order of first ionization enthalpy for them is:

(1) (A) < (B) < (C) < (D)

(2) (B) < (A) < (D) < (C)          

(3) (B) < (D) < (A) < (C)  

(4) (B) < (A) < (C) < (D) 

Ans. (3)

(A) 3s²→ Mg

(B) 3s²3p¹→ Al

(C) 3s²3p³ → P

(D) 3s²3p⁴→ S

Ans. (3)  C > D > A > B.

 P > S > Mg > Al

Q.9 The first ionization enthalpy of Na, Mg and Si, respectively, are: 496, 737 and 786 mo1^-1. The first ionization enthalpy (kJ mol^-1) of Al is:

(1)  487                (2) 768                  (3) 577             (4) 856

Ans. (3)

Sol.   I.E. : Na < Al < Mg < Si

∴  496 < IE (Al) < 737

  i.e. IE(Al) = 577 kJ mol^-1

Q.10 In which of the following pairs, electron gain enthalpies of constituent elements are nearly the same or identical ?

(A)  Rb and Cs       (B) Na and K               (C)  Ar and Kr     (D) I and At

Choose the correct answer from the options given below :

(1)  (A) and (B) only                        (2) (B) and (C) only

(3)  (A) and (C) only                         (4) (C) and (D) only

Ans. (3)

Sol.   Rb & Cs have nearly the same electron gain enthalpy electron gain enthalpy = – 46 kj/ml.

Ar & Kr have the same . Value is ΔH_eq + 96 kj/ml

Q.11.  Match List -I with List - II

Choose the most appropriate answer from the options given below -

(1) (a) → (ii), (b) → (iii), (c)→ (iv), (d) → (i)

(2) (a) → (i), (b) → (iv), (c) → (iii), (d) → (ii)

(3) (a) → (i), (b) → (iii), (c) → (iv), (d) → (ii)

(4) (a) → (iv), (b) → (i), (c) → (ii), (d) → (iii)

Ans. (1)

Sol. (a) 1s²2s² → Be

(b) 1s²2s²2p⁴ → O

(c) 1s²2s²2p³→ N

(d) 1s²2s²2p¹ → B

The ionization enthalpy order is

B < Be < O < N

Be has more IE compared to B due to extra stability & N has more IE compared to oxygen due to extra stability

Hence, N → 1402 kJ/mol

O  → 1314 kJ/mol

B  → 801 k

Be → 899 kJ/mol

Q.12. The ionic radii of F^– and O^2– respectively are 1.33 Å and 1.4 Å, while the covalent radius of N is 0.74 Å. The correct statement for the ionic radius of N^3– from the following is :

(1) It is smaller than F^– and N

(2) It is bigger than O^2– and 

(3) It is bigger than F^– and N, but smaller than of O^2–

(4) It is smaller than O^2– and F^–, but bigger than of N

Ans. (2)

Sol. F^–, O^2– and N^3– all are isoelectronic species in which N^3– have the least number of protons due to which its size increases as least nuclear attraction is experienced by the outer shell electrons.

Size order   N^3– > O^2– > F^–

Q.13 The correct order of conductivity of ions in water is :

(1) Na⁺ > K⁺ > Rb⁺ > Cs⁺                                                                                             

(2) Cs⁺ > Rb⁺ > K⁺ > Na⁺

(3) K⁺ > Na⁺ > Cs⁺ > Rb⁺                                                                                              

(4) Rb⁺ > Na⁺ > K⁺ > Li⁺

Ans.(2) 

Sol. 

∴ Correct option is Na+ > K+ > Rb+ > Cs+.

OR

Sol. 

As the size of gaseous ions decreases, it gets more hydrated in water and hence, the size of aqueous ions increases. When this bulky ion moves in solution, it experiences greater resistance and hence lower conductivity.

Size of gaseous ion : Cs⁺ > Rb⁺ > K⁺ > Na⁺

Size of aqueous ion : Cs⁺ < Rb⁺ < K⁺ < Na⁺

Conductivity : Cs⁺ > Rb⁺ > K⁺ > Na⁺