Atomic Structure MCQs 2026

Atoms having the same number of neutrons but different atomic numbers are called

1. AIsotopes✓
2. BIsobars✓
3. CIsotones✓
4. DIsomers✓

The atomic number of an element represents the number of

1. AProtons in the nucleus✓
2. BNeutrons in the nucleus✓
3. CTotal nucleons✓
4. DValence shells✓

The mass number of an atom is the sum of

1. AProtons and neutrons✓
2. BProtons and electrons✓
3. CNeutrons and electrons✓
4. DProtons only✓

According to the Aufbau principle, electrons fill orbitals

1. AIn order of increasing energy✓
2. BRandomly✓
3. CIn order of decreasing energy✓
4. DOnly in the outermost shell✓

The Pauli exclusion principle states that no two electrons in an atom can have

1. AThe same principal quantum number✓
2. BThe same shape orbital✓
3. CThe same energy✓
4. DThe same set of four quantum numbers✓

Hund's rule of maximum multiplicity states that electrons occupy degenerate orbitals

1. ASingly with parallel spins before pairing✓
2. BIn pairs immediately✓
3. COnly in s-orbitals✓
4. DAccording to atomic mass✓

The principal quantum number (n) determines the

1. AShape of orbital✓
2. BSpin of electron✓
3. CSize and energy of the shell✓
4. DOrientation of orbital✓

The azimuthal (angular momentum) quantum number determines the

1. AEnergy of the shell only✓
2. BShape of the subshell/orbital✓
3. CSpin direction✓
4. DNumber of shells✓

The magnetic quantum number determines the

1. AEnergy of electron✓
2. BShape of orbital✓
3. CSpin of electron✓
4. DOrientation of orbital in space✓

The spin quantum number can have values of

1. A+1/2 and -1/2✓
2. B0 and 1✓
3. C-1, 0, +1✓
4. D1, 2, 3✓

The shape of a p-orbital is

1. ASpherical✓
2. BCubical✓
3. CCircular✓
4. DDumbbell-shaped✓

The shape of an s-orbital is

1. ADumbbell✓
2. BCloverleaf✓
3. CSpherical✓
4. DElliptical✓

The maximum number of electrons a single orbital can hold is

1. A1✓
2. B3✓
3. C2✓
4. D6✓

The number of orbitals in a p-subshell is

1. A1✓
2. B3✓
3. C5✓
4. D7✓

The number of orbitals in a d-subshell is

1. A3✓
2. B1✓
3. C5✓
4. D7✓

Heisenberg's uncertainty principle states that it is impossible to simultaneously determine, with perfect accuracy, an electron's

1. APosition and momentum✓
2. BCharge and mass✓
3. CSpin and charge✓
4. DEnergy and charge✓

The de Broglie equation relates the wavelength of a particle to its

1. ACharge✓
2. BMomentum✓
3. CVolume✓
4. DTemperature✓

The quantum mechanical model of the atom was developed mainly by

1. ABohr✓
2. BRutherford✓
3. CSchrodinger✓
4. DDalton✓

Electron configuration of chromium (Cr, Z=24) is an exception to the Aufbau principle because it is written as

1. A[Ar]3d^4 4s^2✓
2. B[Ar]3d^5 4s^1✓
3. C[Ar]3d^6 4s^0✓
4. D[Ar]4s^2 3d^4✓

Electron configuration of copper (Cu, Z=29) is written as

1. A[Ar]3d^9 4s^2✓
2. B[Ar]4s^2 3d^9✓
3. C[Ar]3d^10 4s^1✓
4. D[Ar]3d^8 4s^2✓

The number of valence electrons in an atom of chlorine (Cl, Z=17) is

1. A7✓
2. B5✓
3. C8✓
4. D1✓

Moseley's experiments on X-ray spectra established the concept of

1. AIsotopes✓
2. BElectron spin✓
3. CNuclear fission✓
4. DAtomic number as a fundamental property✓

An atom that has gained one or more electrons becomes a

1. ACation✓
2. BNeutral atom✓
3. CAnion✓
4. DIsotope✓

The K, L, M, N designations refer to

1. ATypes of orbitals✓
2. BTypes of quantum numbers✓
3. CTypes of subatomic particles✓
4. DPrincipal energy shells (n=1,2,3,4)✓

The relative atomic mass of an atom is expressed in

1. AGrams✓
2. BKilograms✓
3. CAtomic mass units (amu)✓
4. DMoles✓

One atomic mass unit (amu) is defined as 1/12th the mass of an atom of

1. AHydrogen-1✓
2. BOxygen-16✓
3. CCarbon-12✓
4. DHelium-4✓

The number of unpaired electrons in a nitrogen atom (Z=7, 1s^2 2s^2 2p^3) is

1. A1✓
2. B2✓
3. C0✓
4. D3✓

Which of the following pairs represents isotopes

1. ACarbon-12 and Carbon-14✓
2. BCarbon-14 and Nitrogen-14✓
3. CArgon-40 and Potassium-40✓
4. DSodium-23 and Magnesium-23✓

Which pair below is an example of isobars

1. ACarbon-12 and Carbon-14✓
2. BHydrogen-1 and Hydrogen-2✓
3. COxygen-16 and Oxygen-18✓
4. DArgon-40 and Calcium-40✓

The energy of an electron in the nth orbit of a hydrogen atom according to Bohr's model is proportional to

1. An✓
2. Bn^3✓
3. C1/n✓
4. D-1/n^2✓

The phenomenon in which spectral lines split under a magnetic field is called the

1. AZeeman effect✓
2. BCompton effect✓
3. CPhotoelectric effect✓
4. DDoppler effect✓

The total number of subshells present in the third principal shell (n=3) is

1. A2✓
2. B3✓
3. C4✓
4. D1✓

An electron in a 2p orbital has an azimuthal quantum number (l) equal to

1. A0✓
2. B3✓
3. C1✓
4. D2✓

The number of radial nodes in a 2s orbital is

1. A0✓
2. B1✓
3. C2✓
4. D3✓

Which scientist proposed that electrons behave both as particles and waves

1. ARutherford✓
2. BBohr✓
3. CChadwick✓
4. Dde Broglie✓

The electron configuration of a neutral sodium atom (Z=11) is

1. A1s^2 2s^2 2p^5 3s^2✓
2. B1s^2 2s^2 2p^6 3s^1✓
3. C1s^2 2s^2 2p^6 3s^2✓
4. D1s^2 2s^2 2p^4 3s^3✓

The effective nuclear charge experienced by valence electrons generally ___ across a period from left to right

1. AIncreases✓
2. BDecreases✓
3. CRemains constant✓
4. DBecomes zero✓

The shielding (screening) effect is caused mainly by

1. AInner-shell electrons repelling outer electrons from the nucleus's pull✓
2. BNeutrons in the nucleus✓
3. CProtons attracting outer electrons✓
4. DPhotons emitted by the nucleus✓