Structure of Atom

27 JEE Main questions · Chemistry

ChemistryJEE Main 21 Jan 2026, Shift 1·Q20·MCQ·Easy–moderate
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Hydrogen spectrum spectral series
Given below are two statements:
Statement I: When an electric discharge is passed through gaseous hydrogen, the hydrogen molecules dissociate and the energetically excited hydrogen atoms produce electromagnetic radiation of discrete frequencies.
Statement II: The frequency of second line of Balmer series obtained from $\ce{He+}$ is equal to that of first line of Lyman series obtained from hydrogen atom.
In the light of the above statements, choose the correct answer from the options given below:
1. (1)Both Statement I and Statement II are true
2. (2)Both Statement I and Statement II are false
3. (3)Statement I is false but Statement II is true
4. (4)Statement I is true but Statement II is false
ChemistryJEE Main 21 Jan 2026, Shift 2·Q1·MCQ·Easy–moderate
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Hydrogen spectrum spectral series
Consider the following spectral lines for atomic hydrogen:
- (A)First line of Paschen series
- (B)Second line of Balmer series
- (C)Third line of Paschen series
- (D)Fourth line of Brackett series
The correct arrangement of the above lines in ascending order of energy is:
1. (1)D $<$ C $<$ A $<$ B
2. (2)A $<$ B $<$ C $<$ D
3. (3)C $<$ D $<$ B $<$ A
4. (4)D $<$ A $<$ C $<$ B
We corrected a printing error in the original paper
Source printed “Fourth line of Bracket sereis”.
ChemistryJEE Main 22 Jan 2026, Shift 1·Q4·MCQ·Easy–moderate
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Bohr model excitation energy
The energy required by electrons, present in the first Bohr orbit of hydrogen atom to be excited to second Bohr orbit is J mol $^{-1}$ .
Given : $R_\mathrm{H} = 2.18\times10^{-11}$ ergs.
1. (1) $1.635\times10^{-18}$
2. (2) $9.835\times10^{5}$
3. (3) $9.835\times10^{12}$
4. (4) $1.635\times10^{-11}$
ChemistryJEE Main 22 Jan 2026, Shift 2·Q14·MCQ·Easy–moderate
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Hydrogen spectrum balmer series
The energy of first (lowest) Balmer line of H atom is $x$ J. The energy (in J) of second Balmer line of H atom is :
1. (1) $x^2$
2. (2) $\dfrac{x}{1.35}$
3. (3) $2x$
4. (4) $1.35\,x$
ChemistryJEE Main 23 Jan 2026, Shift 1·Q1·MCQ·Easy–moderate
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Bohr model energy levels
Which of the following statements regarding the energy of the stationary state is true in the following one-electron system ?
1. (1) $-1.09\times10^{-18}$ J for second orbit of H atom.
2. (2) $+2.18\times10^{-18}$ J for second orbit of $\ce{He+}$ ion
3. (3) $+8.72\times10^{-18}$ J for first orbit of $\ce{He+}$ ion
4. (4) $-2.18\times10^{-18}$ J for third orbit of $\ce{Li^{2+}}$ ion
ChemistryJEE Main 23 Jan 2026, Shift 1·Q11·MCQ·Easy–moderate
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Quantum numbers
Given,
(A) $n = 5$ , $m_l = -1$
(B) $n = 3$ , $l = 2$ , $m_l = -1$ , $m_s = +\dfrac{1}{2}$
The maximum number of electron(s) in an atom that can have the quantum numbers as given in (A) and (B) respectively are :
1. (1)26 and 1
2. (2)4 and 1
3. (3)2 and 4
4. (4)8 and 1
We corrected a printing error in the original paper
Source printed the magnetic quantum number as “m $_1$ ” and the azimuthal quantum number in (B) as “1 = 2” (digit 1 for l).
ChemistryJEE Main 23 Jan 2026, Shift 2·Q14·MCQ·Easy–moderate
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Atomic notation and photon energy
Identify the INCORRECT statements from the following:
- (A)Notation $\ce{^{24}_{12}Mg}$ represents 24 protons and 12 neutrons.
- (B)Wavelength of a radiation of frequency $4.5\times10^{15}$ s $^{-1}$ is $6.7\times10^{-8}$ m.
- (C)One radiation has wavelength $= \lambda_1$ (900 nm) and energy $= E_1$ . Other radiation has wavelength $= \lambda_2$ (300 nm) and energy $= E_2$ . $E_1 : E_2 = 3 : 1$ .
- (D)Number of photons of light of wavelength 2000 pm that provides 1 J of energy is $1.006\times10^{16}$ .
Choose the correct answer from the options given below:
1. (1)A and D only
2. (2)A and C only
3. (3)A and B only
4. (4)B and C only
ChemistryJEE Main 23 Jan 2026, Shift 2·Q18·MCQ·Easy–moderate
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Photoelectric effect work function
The work functions of two metals ( $\mathrm{M_A}$ and $\mathrm{M_B}$ ) are in the 1 : 2 ratio. When these metals are exposed to photons of energy 6 eV, the kinetic energy of liberated electrons of $\mathrm{M_A : M_B}$ is in the ratio of 2.642 : 1. The work functions (in eV) of $\mathrm{M_A}$ and $\mathrm{M_B}$ are respectively.
1. (1)3.1, 6.2
2. (2)2.3, 4.6
3. (3)1.4, 2.8
4. (4)1.5, 3.0
ChemistryJEE Main 24 Jan 2026, Shift 1·Q23·Numerical·Easy–moderate
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Hydrogen spectrum spectral series
The hydrogen spectrum consists of several spectral lines in Lyman series ( $L_1$ , $L_2$ , $L_3$ …; $L_1$ has lowest energy among Lyman series). Similarly it consists of several spectral lines in Balmer series ( $B_1$ , $B_2$ , $B_3$ …; $B_1$ has lowest energy among Balmer lines). The energy of $L_1$ is $x$ times the energy of $B_1$ . The value of $x$ is $\times\,10^{-1}$ (Nearest integer)
We corrected a printing error in the original paper
Source printed “(Nearest inteter)”.
ChemistryJEE Main 24 Jan 2026, Shift 2·Q13·MCQ·Easy–moderate
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Hydrogen-like spectrum rydberg formula
The wavelength of spectral line obtained in the spectrum of $\ce{Li^2+}$ ion, when the transition takes place between two levels whose sum is 4 and difference is 2, is
1. (1) $2.28\times10^{-7}$ cm
2. (2) $2.28\times10^{-6}$ cm
3. (3) $1.14\times10^{-7}$ cm
4. (4) $1.14\times10^{-6}$ cm
We corrected a printing error in the original paper
Source printed “LI $^{2+}$ ion”.
ChemistryJEE Main 28 Jan 2026, Shift 1·Q16·MCQ·Easy–moderate
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Hydrogen spectrum balmer series
The wave numbers of three spectral lines of H atom are considered. Identify the set of spectral lines belonging to Balmer series.
( $R$ = Rydberg constant)
1. (1) $\dfrac{5R}{36}, \dfrac{3R}{16}, \dfrac{21R}{100}$
2. (2) $\dfrac{5R}{36}, \dfrac{8R}{9}, \dfrac{15R}{16}$
3. (3) $\dfrac{7R}{144}, \dfrac{3R}{16}, \dfrac{16R}{255}$
4. (4) $\dfrac{3R}{4}, \dfrac{3R}{16}, \dfrac{7R}{144}$
ChemistryJEE Main 28 Jan 2026, Shift 1·Q17·MCQ·Easy
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Radial nodes of 2s orbital
Figure 1. electron probability density for 2s orbital
Figure 2. wave function for 2s orbital
Which of the following point in Figure 2 most accurately represents the nodal surface as shown in Figure 1 ?
1. (1)B
2. (2)D
3. (3)C
4. (4)A
ChemistryJEE Main 28 Jan 2026, Shift 2·Q9·MCQ·Easy–moderate
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Photon energy from wavelength and frequency
The wavelength of photon ‘A' is 400 nm. The frequency of photon ‘B' is $10^{16}\,\mathrm{s^{-1}}$ . The wave number of photon ‘C' is $10^{4}\,\mathrm{cm^{-1}}$ . The correct order of energy of these photons is :
1. (1)C $>$ B $>$ A
2. (2)B $>$ A $>$ C
3. (3)A $>$ B $>$ C
4. (4)A $>$ C $>$ B
ChemistryJEE Main 28 Jan 2026, Shift 2·Q21·Numerical·Easy–moderate
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De broglie wavelength of accelerated particles
Two positively charged particles $m_1$ and $m_2$ have been accelerated across the same potential difference of 200 keV as shown below.
[Given mass of $m_1 = 1$ amu and $m_2 = 4$ amu]
The deBroglie wavelength of $m_1$ will be x times of $m_2$ . The value of x is . (nearest integer)
ChemistryJEE Main 2 Apr 2026, Shift 1·Q2·MCQ·Easy–moderate
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Ionisation energy hydrogen-like ions
What is the energy (in J atom $^{-1}$ ) required for the following process ?
$\ce{Li^2+(g) -> Li^3+(g) + e-}$
(Take the ionization energy for the H atom in the ground state as $2.18\times10^{-18}$ J atom $^{-1}$ )
1. (1) $8.72\times10^{-18}$
2. (2) $1.962\times10^{-18}$
3. (3) $1.962\times10^{-17}$
4. (4) $6.54\times10^{-17}$
ChemistryJEE Main 2 Apr 2026, Shift 2·Q21·Numerical·Easy–moderate
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Photoelectric effect
The surface of sodium metal is irradiated with radiation of wavelength x nm. The kinetic energy of ejected electrons is $2.8\times10^{-20}$ J. The work function of sodium is 2.3 eV. The value of x is $\times10^{2}$ nm. (Nearest integer)
(Given : $h = 6.6\times10^{-34}$ J s; 1eV $= 1.60\times10^{-19}$ J; $c = 3.0\times10^{8}$ m s $^{-1}$ )
ChemistryJEE Main 4 Apr 2026, Shift 1·Q2·MCQ·Easy–moderate
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Hydrogen spectrum spectral series
What is the ratio of wave number of first line (lowest energy line) of Balmer series of H atomic spectrum to first line of its Brackett series?
1. (1)5:1
2. (2)5:0.81
3. (3)5:1.75
4. (4)5:27
ChemistryJEE Main 4 Apr 2026, Shift 1·Q3·MCQ·Easy–moderate
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Quantum numbers and aufbau principle
Which of the following is correct set of 4 quantum number of 19 $^\text{th}$ electron in Chromium (Atomic number $=$ 24) in accordance with Aufbau principle?
1. (1) $n = 3$ , $\ell = 2$ , $m = +2$ , $s = +\dfrac{1}{2}$
2. (2) $n = 3$ , $\ell = 2$ , $m = -2$ , $s = +\dfrac{1}{2}$
3. (3) $n = 4$ , $\ell = 1$ , $m = 0$ , $s = +\dfrac{1}{2}$
4. (4) $n = 4$ , $\ell = 0$ , $m = 0$ , $s = +\dfrac{1}{2}$
ChemistryJEE Main 4 Apr 2026, Shift 1·Q8·MCQ·Easy–moderate
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Atomic number and mass number
A monoatomic anion ( $\ce{A^-}$ ) has 45 neutrons and 36 electrons. Atomic mass, group in the periodic table and physical state at room temperature of the element (A) respectively are :
1. (1)80, 17, liquid
2. (2)81, 16, solid
3. (3)80, 16, gas
4. (4)81, 15, gas
ChemistryJEE Main 4 Apr 2026, Shift 2·Q2·MCQ·Easy–moderate
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Bohr model radius of orbit
The species having identical radii according to the Bohr's theory are :
- (A)H (first orbit)
- (B) $\ce{He+}$ (first orbit)
- (C) $\ce{He+}$ (second orbit)
- (D) $\ce{Li^2+}$ (first orbit)
- (E) $\ce{Be^3+}$ (Second orbit)
Choose the correct answer from the options given below :
1. (1)A and C Only
2. (2)A and E Only
3. (3)B and E Only
4. (4)C and D Only
ChemistryJEE Main 5 Apr 2026, Shift 1·Q2·MCQ·Easy–moderate
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Orbital energy n plus l rule
Arrange the following atomic orbitals of multi electron atoms in order of increasing energy.
- (A) $n = 3$ , $\ell = 2$ , $m = +1$
- (B) $n = 4$ , $\ell = 0$ , $m = 0$
- (C) $n = 6$ , $\ell = 1$ , $m = 0$
- (D) $n = 5$ , $\ell = 1$ , $m = +1$
- (E) $n = 2$ , $\ell = 1$ , $m = +1$
Choose the correct answer from the options given below :
1. (1)C $<$ D $<$ B $<$ A $<$ E
2. (2)B $<$ A $<$ E $<$ C $<$ D
3. (3)E $<$ C $<$ D $<$ B $<$ A
4. (4)E $<$ B $<$ A $<$ D $<$ C
ChemistryJEE Main 5 Apr 2026, Shift 1·Q3·MCQ·Easy–moderate
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Uncertainty principle and orbital energies
Identify the correct statements from the following :
- (A)Heisenberg uncertainty principle is applicable to electron.
- (B)The size of 2p $_x$ orbital is less than the size of 3p $_x$ orbital.
- (C)The energy of 2s orbital of H atom is equal to the energy of 2s orbital of Li.
- (D)The electronic configuration of Cr is [Ar] 3d $^5$ 4s $^1$
Choose the correct answer from the options given below :
1. (1)A, B and C only
2. (2)A, B and D only
3. (3)B, C, and D only
4. (4)A, C and D only
ChemistryJEE Main 5 Apr 2026, Shift 2·Q2·MCQ·Easy–moderate
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Orbital energies and radial nodes
Which of the following statement(s) is/are true ?
- (A)If two orbitals have the same value of $(n + l)$ , the orbital with lower value of $n$ will have lower energy.
- (B)Energies of the orbitals in the same subshell increase with increase in atomic number.
- (C)The size of 2p $_x$ orbital is less than the size of 3p $_x$ orbital.
- (D)Among 5f, 6s, 4d, 5p and 5d orbitals, none of the orbitals have 2 radial nodes.
Choose the correct answer from the options given below :
1. (1)A, B and C only
2. (2)A and C only
3. (3)C and D only
4. (4)A only
ChemistryJEE Main 6 Apr 2026, Shift 1·Q2·MCQ·Easy–moderate
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Hydrogen spectrum series wavelengths
If shortest wavelength of hydrogen atom in Lyman series is x, then longest wavelength in Balmer series of $\ce{He+}$ is :
1. (1) $\dfrac{9x}{5}$
2. (2) $\dfrac{36x}{5}$
3. (3) $\dfrac{x}{4}$
4. (4) $\dfrac{5x}{9}$

ChemistryJEE Main 6 Apr 2026, Shift 1·Q3·MCQ·Easy–moderate

Radial and angular nodes

Match the List-I with List-II :

List-I		List-II
Orbital		Radial nodes and nodal plane
A.	2s	I.	1 Radial node + two nodal planes
B.	3s	II.	1 Radial node + one nodal plane
C.	3p	III.	2 Radial nodes + No nodal plane
D.	4d	IV.	1 Radial node + No nodal plane.

Choose the correct answer from the options given below :

(1)A-IV, B-I, C-III, D-II
(2)A-IV, B-II, C-III, D-I
(3)A-III, B-I, C-IV, D-II
(4)A-IV, B-III, C-II, D-I

ChemistryJEE Main 6 Apr 2026, Shift 2·Q2·MCQ·Easy–moderate
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Bohr radius hydrogen like species
The Bohr radius of a hydrogen like species is 70.53 pm. The species and the stationary state(n) are respectively
(Given: Hydrogen atom Bohr radius is 52.9 pm)
1. (1) $\ce{Li^{2+}}$ , 3
2. (2) $\ce{He+}$ , 3
3. (3) $\ce{He+}$ , 2
4. (4) $\ce{Li^{2+}}$ , 2
ChemistryJEE Main 8 Apr 2026, Shift 2·Q23·Numerical·Easy
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Photon energy and wavelength
Consider two radiations of wavelengths :
1. $\lambda_1 = 2000$ Å
2. $\lambda_2 = 6000$ Å
The ratio of the energies of these two radiations $\left(\dfrac{E_1}{E_2}\right)$ is . (Nearest integer)