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Which of the following is the smallest particle of an element that retains its chemical identity and participates in chemical reactions?
किसी तत्व का वह सूक्ष्मतम कण कौन सा है जो रासायनिक अभिक्रियाओं में भाग लेता है और अपनी रासायनिक पहचान बनाए रखता है?
(A) Molecule
(B) Atom (Paramaanu)
(C) Quark
(D) Nucleon
✅ Answer & Explanation
Sahi jawab: B) Atom (Paramaanu)Explanation: Dalton ke mutabiq Atom kisi element ka sabse chhota particle hai jo chemical reaction me hissa leta hai; subatomic particles hote zaroor hain par wo element ki chemical identity represent nahi karte.
Who discovered the subatomic, negatively charged 'Electron' in 1897 through Cathode Ray Tube (CRT) experiments?
1897 में कैथोड किरण नलिका (CRT) प्रयोगों के माध्यम से ऋणावेशित 'इलेक्ट्रॉन' की खोज किसने की थी?
(A) Ernest Rutherford
(B) J.J. Thomson
(C) James Chadwick
(D) Eugen Goldstein
✅ Answer & Explanation
Sahi jawab: B) J.J. ThomsonExplanation: J.J. Thomson ne cathode ray discharge tube me negative particles discover kiye jinhe George Stoney ne 'Electron' naam diya; Thomson ne electron ka charge-to-mass (e/m) ratio bhi nikala.
The central, dense 'Nucleus' of an atom discovered by Rutherford consists of which subatomic nucleons?
परमाणु के केंद्रीय नाभिक (Nucleus) में कौन से उप-परमाण्विक कण (न्यूक्लिऑन) पाए जाते हैं?
(A) Electrons and Protons
(B) Protons and Neutrons (Nucleons)
(C) Electrons and Neutrons
(D) Positrons only
✅ Answer & Explanation
Sahi jawab: B) Protons and Neutrons (Nucleons)Explanation: Atom ke center me positively charged dense nucleus hota hai jisme Protons aur Neutrons (dono ko milakar Nucleons bolte hain) rehte hain, jabki electrons chaaron taraf orbits me ghoomte hain.
What is the fundamental unit electric charge and resting mass of an individual Proton?
एक प्रोटॉन पर कितना धनात्मक विद्युत आवेश और द्रव्यमान होता है?
(A) -1.6 x 10^-19 C
(B) +1.602 x 10^-19 C (Mass: 1.672 x 10^-27 kg)
(C) Zero charge (Neutral)
(D) +3.2 x 10^-19 C
✅ Answer & Explanation
Sahi jawab: B) +1.602 x 10^-19 C (Mass: 1.672 x 10^-27 kg)Explanation: Proton par positive charge (+1.6 x 10^-19 Coulomb) hota hai aur iska mass lagbhag 1 amu hota hai, jo electron ke mass se 1,837 guna heavy hota hai.
Who proposed the first scientific 'Atomic Theory' in 1803 postulating that matter is composed of indivisible atoms?
1803 में सर्वप्रथम वैज्ञानिक 'परमाणु सिद्धांत' का प्रतिपादन किसने किया था जिसमें परमाणुओं को अविभाज्य बताया गया था?
(A) Amedeo Avogadro
(B) John Dalton
(C) Antoine Lavoisier
(D) Niels Bohr
✅ Answer & Explanation
Sahi jawab: B) John DaltonExplanation: John Dalton ne Law of Conservation of Mass aur Constant Proportions ke aadhar par Atomic Theory di thi ki matter indestructible aur indivisible chote atoms se bana hai.
The 'Mass Number' (A) of any atomic nucleus is mathematically defined as the:
किसी परमाणु की 'द्रव्यमान संख्या' (Mass Number - A) किसे दर्शाती है?
(A) Total number of planetary electrons
(B) Total number of protons only (Atomic Number Z)
(C) Total sum of Protons and Neutrons (Nucleons: A = Z + N)
(D) Number of valence electrons
✅ Answer & Explanation
Sahi jawab: C) Total sum of Protons and Neutrons (Nucleons: A = Z + N)Explanation: Mass Number (A) nucleus ke andar baithe Protons aur Neutrons ka total sum hota hai (A = Z + N); electron ka mass itna kam hota hai ki use atomic mass me count nahi karte.
Nuclides of the same chemical element sharing an identical Atomic Number (Z) but differing in Mass Number (A) are termed:
एक ही तत्व के वे परमाणु जिनका परमाणु क्रमांक (Z) समान लेकिन द्रव्यमान संख्या (A) भिन्न होती है, क्या कहलाते हैं?
(A) Isobars
(B) Isotopes (Samsthaanik)
(C) Isotones
(D) Isodiaphers
✅ Answer & Explanation
Sahi jawab: B) Isotopes (Samsthaanik)Explanation: Isotopes me protons aur electrons barabar hote hain (isliye chemical properties same hoti hain), par unme neutrons ki sankhya alag-alag hoti hai (jaise Carbon-12 aur Carbon-14).
Which rare isotope of Hydrogen contains two neutrons and is unstable and radioactive in nature?
हाइड्रोजन का कौन सा समस्थानिक (Isotope) प्राकृतिक रूप से अस्थिर और रेडियोधर्मी (Radioactive) होता है?
(A) Protium (1H1)
(B) Deuterium (2H1)
(C) Tritium (3H1)
(D) Hydronium
✅ Answer & Explanation
Sahi jawab: C) Tritium (3H1)Explanation: Hydrogen ke 3 isotopes hain: Protium (0 neutron), Deuterium (1 neutron, heavy water banata hai), aur Tritium (2 neutrons), jo beta radiation chhodne wala radioactive isotope hai.
Who discovered the neutral, uncharged subatomic particle 'Neutron' in 1932 by bombarding beryllium with alpha particles?
1932 में बेरिलियम पर अल्फा कणों की बमबारी करके अनावेशित 'न्यूट्रॉन' की खोज किसने की थी?
(A) Ernest Rutherford
(B) James Chadwick
(C) J.J. Thomson
(D) Eugen Goldstein
✅ Answer & Explanation
Sahi jawab: B) James ChadwickExplanation: James Chadwick ne Beryllium foil par Alpha particles se attack karwaya jisse bina charge wale neutral particles nikle jinhe 'Neutron' naam diya gaya.
Ernest Rutherford's iconic 1911 Gold Foil Alpha-Particle Scattering Experiment conclusively proved the existence of:
1911 में रदरफोर्ड के सोने की पन्नी पर अल्फा कण प्रकीर्णन प्रयोग ने परमाणु में किसकी खोज की?
(A) Planetary energy subshells
(B) The tiny, dense, positively charged Atomic Nucleus
(C) Electrons in raisins
(D) Wave nature of matter
✅ Answer & Explanation
Sahi jawab: B) The tiny, dense, positively charged Atomic NucleusExplanation: Rutherford ne dekha ki 20,000 me se 1 alpha particle 180° par wapas takra kar lauta, jisse prove hua ki atom ka poora positive charge center me ek tiny dense Nucleus me concentrated hai.
According to the Bohr-Bury scheme, what is the maximum electron capacity of any principal shell with quantum index 'n'?
बोर-बरी योजना के अनुसार किसी भी मुख्य कोश (Shell) में इलेक्ट्रॉनों की अधिकतम संख्या किस सूत्र से ज्ञात की जाती है?
(A) 2n
(B) 2n^2 (e.g., K=2, L=8, M=18, N=32)
(C) n^2
(D) 4n + 2
✅ Answer & Explanation
Sahi jawab: B) 2n^2 (e.g., K=2, L=8, M=18, N=32)Explanation: Formula 2n^2 hota hai: K-shell (n=1) me 2(1)^2 = 2; L-shell (n=2) me 2(2)^2 = 8; M-shell (n=3) me 18; aur N-shell (n=4) me maximum 32 electrons aa sakte hain.
The thermodynamic phase transition where a solid converts directly into the gaseous vapor phase without melting into a liquid is:
ठोस पदार्थ का बिना द्रव में बदले सीधे वाष्प (गैस) में परिवर्तित हो जाने की प्रक्रिया क्या कहलाती है?
(A) Evaporation
(B) Condensation
(C) Sublimation (Urdhwapaatan)
(D) Deposition
✅ Answer & Explanation
Sahi jawab: C) Sublimation (Urdhwapaatan)Explanation: Sublimation me garam karne par solid direct gas ban jata hai; jaise Camphor (Kapoor), Dry Ice (Solid CO2), Ammonium Chloride (Naushadar) aur Naphthalene balls.
Which high-energy state of matter comprises superheated, quasi-neutral, freely moving ionized gases and stripped electrons?
तारों और सूर्य में पाई जाने वाली अत्यधिक गर्म आयनित गैस और मुक्त इलेक्ट्रॉनों से युक्त 'पदार्थ की चौथी अवस्था' कौन सी है?
(A) Gas
(B) Plasma
(C) Bose-Einstein Condensate (BEC)
(D) Fermionic condensate
✅ Answer & Explanation
Sahi jawab: B) PlasmaExplanation: Plasma matter ki 4th state hai jisme extreme heat ki wajah se atoms toot kar positive ions aur free electrons ka ionized soup ban jate hain (jaise Sun, Stars aur Neon signs me).
Atoms of different chemical elements that share the same Mass Number (A) but possess different Atomic Numbers (Z) are:
भिन्न-भिन्न तत्वों के वे परमाणु जिनके परमाणु क्रमांक भिन्न परंतु द्रव्यमान संख्या समान होती है, क्या कहलाते हैं?
(A) Isotopes
(B) Isobars (Sam-bhaarik)
(C) Isotones
(D) Isomers
✅ Answer & Explanation
Sahi jawab: B) Isobars (Sam-bhaarik)Explanation: Isobars alag-alag elements hote hain jinka total mass same hota hai; jaise Argon (18Ar40), Potassium (19K40) aur Calcium (20Ca40) teeno ka mass 40 hai par atomic number alag hai.
Heisenberg's Uncertainty Principle mathematically states that it is physically impossible to simultaneously determine with precision both:
हाइजेनबर्ग के अनिश्चितता सिद्धांत (Uncertainty Principle) के अनुसार किसी सूक्ष्म कण की किन दो राशियों को एक साथ सटीक नहीं मापा जा सकता?
(A) Energy and wavelength
(B) Exact Position (Δx) and Linear Momentum (Δp) of an electron: Δx · Δp ≥ h / (4π)
(C) Mass and velocity
(D) Charge and spin
✅ Answer & Explanation
Sahi jawab: B) Exact Position (Δx) and Linear Momentum (Δp) of an electron: Δx · Δp ≥ h / (4π)Explanation: Heisenberg ne bataya ki electron jaise tiny wave-like particle ki exact position aur exact momentum (speed) ek sath 100% accuracy se measure karna physics ke laws ke mutabiq impossible hai.
What is the physical charge and compositional nature of an ionizing Alpha (α) particle emitted in radioactive decay?
रेडियोधर्मी क्षय में उत्सर्जित होने वाले अल्फा (α) कण की संरचना और आवेश क्या होता है?
(A) -1 charge (single electron)
(B) 0 charge (electromagnetic photon)
(C) +2 charge (doubly ionized Helium nucleus: He2+ with 2 protons and 2 neutrons)
(D) +1 charge
✅ Answer & Explanation
Sahi jawab: C) +2 charge (doubly ionized Helium nucleus: He2+ with 2 protons and 2 neutrons)Explanation: Alpha particle actually ek Helium nucleus (He2+) hota hai jisme 2 protons aur 2 neutrons hote hain; ispar +2 unit positive charge aur 4 amu mass hota hai.
Which orbital quantum number primarily defines the average spatial size and principal energy level of an electron shell?
कौन सी मुख्य क्वांटम संख्या (Principal Quantum Number - n) कक्षक के औसत आकार और मुख्य ऊर्जा स्तर को निर्धारित करती है?
(A) Principal Quantum Number (n)
(B) Azimuthal Quantum Number (l)
(C) Magnetic Quantum Number (ml)
(D) Spin Quantum Number (ms)
✅ Answer & Explanation
Sahi jawab: A) Principal Quantum Number (n)Explanation: Principal quantum number (n = 1, 2, 3...) electron ke main shell ka size aur energy level decide karta hai; jaise-jaise n badhta hai, orbital ka aakaar bada hota jata hai.
Which quantum number dictates the three-dimensional geometric shape (s=spherical, p=dumbbell, d=double-dumbbell) of an atomic subshell?
द्विगंशी क्वांटम संख्या (Azimuthal Quantum Number - l) कक्षक के किस गुण को निर्धारित करती है?
(A) Total shell electron capacity only
(B) Three-dimensional spatial shape and orbital angular momentum (l = 0 to n-1)
(C) Direction of axial magnetic vector
(D) Clockwise electron spin
✅ Answer & Explanation
Sahi jawab: B) Three-dimensional spatial shape and orbital angular momentum (l = 0 to n-1)Explanation: Azimuthal quantum number (l) subshell ki 3D shape batata hai: l=0 (s-orbital, spherical), l=1 (p-orbital, dumbbell), l=2 (d-orbital, double-dumbbell) aur l=3 (f-orbital, complex leaf).
What is the physical significance of the Magnetic Quantum Number (ml) when atoms are placed in external magnetic fields?
चुंबकीय क्वांटम संख्या (Magnetic Quantum Number - ml) कक्षक के किस लक्षण को दर्शाती है?
(A) Total energy eigenvalues
(B) Spatial orientation of orbitals along three-dimensional coordinate axes (ml = -l to +l)
(C) Nuclear fusion threshold
(D) Linear velocity
✅ Answer & Explanation
Sahi jawab: B) Spatial orientation of orbitals along three-dimensional coordinate axes (ml = -l to +l)Explanation: Magnetic quantum number (ml) space me orbital ke orientation (direction) ko batata hai; ye explain karta hai ki p-subshell ke 3 orbitals px, py aur pz axes par kaise situated hain (Zeeman Effect).
Pauli's Exclusion Principle states that no two electrons in the same atom can possess the identical set of four quantum numbers, meaning:
पाउली के अपवर्जन सिद्धांत (Pauli's Exclusion Principle) का मुख्य निष्कर्ष क्या है?
(A) Electrons always fill the highest energy orbitals first
(B) An individual orbital can hold a maximum of two electrons, and they must have anti-parallel (opposite) spins (+1/2 and -1/2)
(C) Orbitals must remain completely degenerate
(D) All electrons repel the nucleus
✅ Answer & Explanation
Sahi jawab: B) An individual orbital can hold a maximum of two electrons, and they must have anti-parallel (opposite) spins (+1/2 and -1/2)Explanation: Pauli ne kaha ki ek atom me do electrons ke chaaron quantum numbers same nahi ho sakte; isliye ek single orbital me maximum 2 electrons hi aa sakte hain aur unka spin ulta (+1/2 aur -1/2) hona chahiye.
The Aufbau Principle ($(n+l)$ rule) dictates that incoming ground-state electrons sequentially occupy orbitals in order of:
आफबाऊ सिद्धांत (Aufbau Principle) के अनुसार इलेक्ट्रॉन कक्षकों में किस क्रम में प्रवेश करते हैं?
(A) Decreasing orbital size
(B) Increasing orbital energy levels: lower (n+l) values fill first before higher ones
(C) Alphabetical subshell sequence
(D) Random probability matrix
✅ Answer & Explanation
Sahi jawab: B) Increasing orbital energy levels: lower (n+l) values fill first before higher onesExplanation: Aufbau German word hai jiska matlab 'construction' hai; electrons pehle sabse kam energy wale (n+l) orbital me ghuste hain; isliye 4s (4+0=4) pehle bharta hai aur 3d (3+2=5) baad me.
Hund's Rule of Maximum Multiplicity establishes that when filling degenerate orbitals of equal energy (like px, py, pz):
हुंड के अधिकतम बहुलता के नियम (Hund's Rule) के अनुसार समान ऊर्जा वाले कक्षकों में इलेक्ट्रॉनों का युग्मन (Pairing) कब शुरू होता है?
(A) Electrons pair up immediately in the first orbital
(B) Each degenerate orbital is singly occupied with parallel spins before any pairing occurs
(C) Electrons drop into the nucleus
(D) Only spin-down electrons enter
✅ Answer & Explanation
Sahi jawab: B) Each degenerate orbital is singly occupied with parallel spins before any pairing occursExplanation: Hund's rule kehta hai ki barabar energy wale degenerate orbitals (jaise 3 p-orbitals) me pehle sabhi me 1-1 electron parallel spin ke sath jayega, uske baad hi pairing shuru hogi taaki repulsion kam ho.
Why do ground-state Chromium (Z=24) and Copper (Z=29) atoms show anomalous configurations ($Cr: [Ar] 3d^5 4s^1$ and $Cu: [Ar] 3d^{10} 4s^1$)?
क्रोमियम ($Z=24$) और कॉपर ($Z=29$) के इलेक्ट्रॉनिक विन्यास में 4s कक्षक से एक इलेक्ट्रॉन 3d कक्षक में क्यों चला जाता है?
(A) To escape relativistic mass effects
(B) Exactly half-filled ($3d^5$) and fully-filled ($3d^{10}$) d-subshells exhibit extra stability due to structural symmetry and high exchange energy
(C) Because the 4s orbital collapses into the nucleus
(D) Due to loss of nuclear charge
✅ Answer & Explanation
Sahi jawab: B) Exactly half-filled ($3d^5$) and fully-filled ($3d^{10}$) d-subshells exhibit extra stability due to structural symmetry and high exchange energyExplanation: Cr aur Cu me 4s se ek electron 3d me chala jata hai kyunki exactly half-filled (3d5) aur completely filled (3d10) subshells bohot symmetric aur extra stable hote hain high exchange energy ki wajah se.
What is the formula to calculate the total number of Radial Nodes and Angular Nodes in an atomic wave function?
किसी कक्षक में रेडियल नोड्स (Radial Nodes) और कोणीय नोड्स (Angular Nodes) ज्ञात करने का सही सूत्र क्या है?
(A) Radial nodes = n, Angular nodes = l
(B) Radial nodes = (n - l - 1), Angular nodes = l, Total nodes = (n - 1)
(C) Radial nodes = l, Angular nodes = n - 1
(D) Radial nodes = 2l + 1, Angular nodes = n
✅ Answer & Explanation
Sahi jawab: B) Radial nodes = (n - l - 1), Angular nodes = l, Total nodes = (n - 1)Explanation: Node wo jagah hai jahan electron milne ki probability zero hoti hai: Angular nodes hamesha l ke barabar hote hain, Radial nodes = (n - l - 1) hote hain, aur Total nodes = (n - 1) hote hain.
How many total, radial, and angular nodes are present in a 3p atomic orbital?
एक 3p कक्षक (3p orbital) में कुल नोड्स, रेडियल नोड्स और कोणीय नोड्स की संख्या क्रमशः कितनी होती है?
(A) Total = 3, Radial = 2, Angular = 1
(B) Total = 2, Radial = 1, Angular = 1 (Since n=3, l=1)
(C) Total = 2, Radial = 2, Angular = 0
(D) Total = 1, Radial = 0, Angular = 1
✅ Answer & Explanation
Sahi jawab: B) Total = 2, Radial = 1, Angular = 1 (Since n=3, l=1)Explanation: 3p orbital ke liye n=3 aur l=1 hota hai. Angular nodes = l = 1; Radial nodes = n - l - 1 = 3 - 1 - 1 = 1; Total nodes = n - 1 = 3 - 1 = 2 hote hain.
Nuclides belonging to different chemical elements possessing the EXACT same number of Neutrons (A - Z) are:
भिन्न-भिन्न तत्वों के वे परमाणु जिनमें न्यूट्रॉनों की संख्या (A - Z) बिल्कुल समान होती है, क्या कहलाते हैं?
(A) Isotopes
(B) Isobars
(C) Isotones (Sam-neutronic)
(D) Isomers
✅ Answer & Explanation
Sahi jawab: C) Isotones (Sam-neutronic)Explanation: Isotones me Neutrons barabar hote hain; jaise Silicon (14Si30, 30-14=16 neutrons), Phosphorus (15P31, 31-15=16 neutrons) aur Sulfur (16S32, 32-16=16 neutrons).
What are 'Isodiaphers' in nuclear physics?
परमाणु भौतिकी में 'आइसोडायफर्स' (Isodiaphers) किन्हें कहा जाता है?
(A) Atoms with equal mass numbers
(B) Nuclides possessing the identical difference between neutrons and protons: (N - Z) or (A - 2Z)
(C) Atoms with the same nuclear charge
(D) Molecules with mirror symmetry
✅ Answer & Explanation
Sahi jawab: B) Nuclides possessing the identical difference between neutrons and protons: (N - Z) or (A - 2Z)Explanation: Isodiaphers wo nuclides hote hain jinme neutrons aur protons ka farq (N - Z) barabar hota hai; jaise Uranium-238 (146 - 92 = 54) aur Thorium-234 (144 - 90 = 54).
Species (atoms, ions, or molecules) that possess the exact same total number of electrons are classified as:
वे परमाणु या आयन जिनमें इलेक्ट्रॉनों की कुल संख्या बिल्कुल समान होती है, क्या कहलाते हैं?
(A) Isotopes
(B) Isoelectronic Species (e.g., N3-, O2-, F-, Ne, Na+, Mg2+, Al3+ all have 10 electrons)
(C) Isobars
(D) Isotones
✅ Answer & Explanation
Sahi jawab: B) Isoelectronic Species (e.g., N3-, O2-, F-, Ne, Na+, Mg2+, Al3+ all have 10 electrons)Explanation: Isoelectronic species me electrons barabar hote hain; jaise Na+ (11-1=10), Mg2+ (12-2=10), F- (9+1=10) aur Neon gas (10) sabhi ke paas 10 electrons hote hain.
Why are transition metal ions like $Fe^{3+}$ ($3d^5$, 5 unpaired electrons) strongly Paramagnetic while $Zn^{2+}$ ($3d^{10}$) is Diamagnetic?
Fe3+ आयन चुंबकीय क्षेत्र में आकर्षित (अनुचुंबकीय) क्यों होता है जबकि Zn2+ आयन प्रतिकर्षित (प्रतिचुंबकीय) होता है?
(A) Fe3+ has higher nuclear mass
(B) Paramagnetism is produced by unpaired electrons possessing net magnetic moments, whereas diamagnetic species have all electrons paired up
(C) Zn2+ has no d-orbitals
(D) Fe3+ expels alpha particles
✅ Answer & Explanation
Sahi jawab: B) Paramagnetism is produced by unpaired electrons possessing net magnetic moments, whereas diamagnetic species have all electrons paired upExplanation: Fe3+ (3d5) me 5 unpaired electrons hote hain jo magnetic field me attract hote hain (Paramagnetic); jabki Zn2+ (3d10) me sabhi electrons paired hote hain jo magnetic field se repel hote hain (Diamagnetic).
The 'Spin-Only' magnetic moment (μ) of a transition metal ion is calculated in Bohr Magnetons (BM) using which formula?
अयुग्मित इलेक्ट्रॉनों (n) वाले किसी संक्रमण धातु आयन का चुंबकीय आघूर्ण (Magnetic Moment - μ) किस सूत्र से निकाला जाता है?
(A) μ = n(n + 1)
(B) μ = √[n(n + 2)] Bohr Magnetons (BM)
(C) μ = √(n + 2)
(D) μ = 2n + 1
✅ Answer & Explanation
Sahi jawab: B) μ = √[n(n + 2)] Bohr Magnetons (BM)Explanation: Spin-only magnetic moment formula μ = √[n(n+2)] BM hota hai; agar n=3 unpaired electrons honge to μ = √[3(3+2)] = √15 ≈ 3.87 Bohr Magneton aayega.