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NEET Chemistry MCQ
Quiz 1
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Q.1
which of the following statement is not correct for an electron that has quantum number n=4 and m=2?
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The electron may have the quantum number s= +1/2
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The electron may have the quantum number l=2
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The electron may have the quantum number l=3
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The electron may have the quantum number l=0,1,2,3
Explanation
Since |m| can never exceed l, a magnetic quantum number of m = 2 requires l to be at least 2 — so l = 2 or l = 3 are both valid (consistent with n = 4, since l must also be less than n), and s = +1/2 is always independently allowed. But claiming l could be 0 or 1 as well (as "l = 0,1,2,3") is wrong, since l = 0 or l = 1 can't accommodate m = 2 at all.
Q.2
Any p -orbital can accommodate up to
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Four electrons
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two electrons with parallel spin
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Two electrons with opposite spin
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six electrons
Explanation
By the Pauli exclusion principle, any single orbital (including any one p-orbital) can hold at most 2 electrons, and those two must have opposite spins.
Q.3
which of the following is incorrect?
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Unpaired electrons in Iron are 4
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Unpaired electrons in titanium are 3
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Unpaired electrons in Chromium are 6
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Unpaired electrons in cobalt are 3
Explanation
Titanium (Ti, [Ar]3d²4s²) has only 2 unpaired electrons in its d² configuration (both d-electrons singly occupy separate orbitals under Hund's rule) — not 3. (Iron [Ar]3d⁶4s² does have 4 unpaired d-electrons; chromium's special [Ar]3d⁵4s¹ configuration does give 6 unpaired electrons total; and cobalt [Ar]3d⁷4s² does have 3 unpaired d-electrons — those three statements are correct.)
Q.4
Identify the pairs which are not of isotopes?
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$^{14}_{6}X$,$^{15}_{6}Y$
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$^{10}_{4}X$,$^{10}_{5}Y$
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$^{36}_{18}X$,$^{37}_{18}Y$
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$^{12}_{6}X$,$^{13}_{6}Y$
Explanation
Isotopes must share the same atomic number (proton count) while differing in mass number. The pair ¹⁰₄X and ¹⁰₅Y has DIFFERENT atomic numbers (4 vs 5) despite sharing the same mass number — that makes them isobars, not isotopes. (The other three pairs all share the same atomic number with different mass numbers, so they genuinely are isotope pairs.)
Q.5
Bohr’s model can explain
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the solar spectrum
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spectrum of atom or ion containing one electron only
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The spectrum of hydrogen atom
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The spectrum of hydrogen molecule
Explanation
Bohr's model correctly predicts the spectrum for any atom or ion that has exactly one electron (hydrogen itself, or hydrogen-like ions such as He⁺, Li²⁺, etc.) — it breaks down for any system with more than one electron, due to electron-electron interactions the model doesn't account for.
Q.6
Rutherford’s experiment on scattering of particles showed for the first that atom has
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Nucleus
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electron
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Proton
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Neutron
Explanation
Rutherford's gold-foil scattering experiment revealed that most of an atom's mass and all of its positive charge are concentrated in a tiny, dense central nucleus — the first direct evidence for the nucleus's existence.
Q.7
The nucleus of the element having atomic number 25 and atomic weight 55 will contain
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55 neutrons
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25 protons and 30 neutrons
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55 protons
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25 neutrons and 30 protons
Explanation
Protons = atomic number = 25. Neutrons = atomic weight − protons = 55 − 25 = 30.
Q.8
which one of the following pair of atoms /atoms-ion have identical ground state configuration
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F+ and Ne
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Li+ and He+
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Cl- and Ar
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Na and K
Explanation
Cl⁻ has 17 + 1 = 18 electrons, and Ar has 18 electrons — identical electron counts and configuration ([Ne]3s²3p⁶). (F⁺ has 8 electrons vs Ne's 10; Li⁺ has 2 electrons vs He⁺'s 1; Na and K sit in different shells entirely — none of these other pairs match.)
Q.9
For a principal Quantum number n=4, which of the following is incorrect
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Total number of subshells are 4
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Total orbitals present is 16
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None of these
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The max number of electrons it can have is 32
Explanation
For n = 4: number of subshells = n = 4 (l = 0,1,2,3), total orbitals = n² = 16, and maximum electrons = 2n² = 32 — all three statements given are actually correct, so none of them is the incorrect one.
Q.10
Match the column
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p -> iv, q -> iii, r -> ii, s-> i
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p -> i, q -> iii, r -> ii, s-> iv
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p -> iii, q -> ii, r -> iv, s-> i
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p -> ii, q -> iii, r -> iv, s-> i
Explanation
Matching each principle to its description: (p) Hund's Rule — pairing doesn't occur until each orbital is singly occupied → (iii) (q) Aufbau Principle — orbitals fill in order of increasing energy → (ii) (r) Pauli Exclusion Principle — no two electrons share the same four quantum numbers → (iv) (s) Heisenberg's Uncertainty Principle — position and momentum can't both be known exactly → (i) So: p → iii, q → ii, r → iv, s → i.
Q.11
Match the column
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p -> ii, q -> iii, r -> iv, s-> i
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p -> iv, q -> iii, r -> ii, s-> i
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p -> i, q -> iii, r -> ii, s-> iv
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p -> ii, q -> i, r -> iv, s-> iii
Explanation
Matching each quantum number to what it determines: (p) Principal quantum number (n) — energy and size of the orbital → (iv) (q) Azimuthal quantum number (l) — shape of the orbital → (iii) (r) Magnetic quantum number (m) — orientation of the orbital → (ii) (s) Spin quantum number (s) — spin of the electron → (i) So: p → iv, q → iii, r → ii, s → i.
Q.12
No two electron in an atom can have
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the same azimuthal quantum numbers
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the same principal quantum numbers
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same magnetic quantum numbers
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an identical set of four quantum numbers
Explanation
The Pauli exclusion principle states that no two electrons in the same atom can share an identical set of all four quantum numbers (n, l, m, and s) — at least one must differ.
Q.13
An electron has a spin quantum number ½ and a magnetic quantum number -1.it cannot be present in
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d -orbital
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s -orbital
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f -orbital
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p -orbital
Explanation
An s-orbital has azimuthal quantum number l = 0, and the magnetic quantum number m can only range from −l to +l — for l = 0, that means m can only be 0. So m = −1 is impossible for an s-orbital (though it's perfectly valid for p, d, or f orbitals, which have larger l).
Q.14
Which of the following is responsible to rule out the existence of definite paths or trajectories of electrons?
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Aufbau principle.
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Heisenberg’s uncertainty principle.
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Pauli’s exclusion principle
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Hund’s rule of maximum multiplicity.
Explanation
Heisenberg's uncertainty principle — which states that a particle's exact position and exact momentum cannot both be known simultaneously — is what rules out the idea of electrons following sharply defined paths or trajectories, replacing that picture with probability distributions (orbitals) instead.
Q.15
The ground state configuration of Fe3+ ion in gaseous state is ( Atomic Number of Fe=26)
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[Ar]18 3d6
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[Ar]18 3d5
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[Ar]18 3d6 4s2
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[Ar]18 3d3 4s2
Explanation
Neutral Fe ([Ar]3d⁶4s²) forms Fe³⁺ by losing 3 electrons — and electrons are always removed from the outermost (4s) subshell before the inner (3d) subshell. Removing both 4s electrons and one 3d electron leaves [Ar]3d⁵ — a stable, half-filled d-subshell configuration.
Q.16
Cathode rays are
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electromagnetic waves
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Stream of electrons
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Streams of positrons
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Stream of alpha particles
Explanation
Cathode rays, discovered in vacuum-tube discharge experiments (notably by J.J. Thomson, leading to the discovery of the electron), are streams of negatively charged electrons.
Q.17
what is the relation for Uncertainty principle
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$E=mc^2$
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$\Delta x \times \Delta p = \frac {h}{8 \pi}$
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$\lambda = \frac {h}{p}$
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$\Delta x \times \Delta p = \frac {h}{2 \pi}$
Explanation
Heisenberg's uncertainty principle relates the uncertainties in position and momentum as Δx × Δp ≥ h/(2π).
Q.18
The pair of ions having same electronic configuration is __________.
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$Fe^{3+}$, $Mn^{2+}$
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$Fe^{3+}$, $Co^{3+}$
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$Sc^{3+}$, $Cr^{3+}$
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$Cr^{3+}$, $Fe^{3+}$
Explanation
Fe³⁺ (26 − 3 = 23 electrons) has configuration [Ar]3d⁵, and Mn²⁺ (25 − 2 = 23 electrons) also has configuration [Ar]3d⁵ — both give the same 23-electron, half-filled-d5 configuration.
Q.19
electromagnetic radiation with maximum wavelength is
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Infrared
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X -rays
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Radio wave
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Ultraviolet
Explanation
Among the electromagnetic spectrum, ordered by increasing wavelength: X-rays < ultraviolet < visible < infrared < radio waves. Radio waves have by far the longest wavelength (and lowest frequency) of these options.
Q.20
Two atoms are said to be isobars if.
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they have same number of neutrons but different number of electrons.
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they have same number of electrons but different number of neutrons.
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sum of the number of protons and neutrons is same but the number of protons is different.
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they have same atomic number but different mass number.
Explanation
Isobars are atoms of different elements (different atomic/proton numbers) that happen to share the same mass number (protons + neutrons total).
0 h : 0 m : 1 s
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