Free Atomic Structure MCQs with Answers

• A. 3d
• B. 4s
• C. 4p
• D. 4d

Explanation: For 4s the sum is 4 plus 0, that is 4, while for 3d it is 3 plus 2, that is 5, so the lower sum fills first and 4s is occupied before 3d.

• A. 1s2 2s2 2p6 3s2 3p5
• B. 1s2 2s2 2p6 3s2 3p6
• C. 1s2 2s2 2p6 3s2 3p4
• D. 1s2 2s2 2p6 3s1

Explanation: Chlorine gains one electron to form the chloride ion, taking its total to 18 and giving it the argon configuration with a complete octet.

• A. electrons can occupy any orbit
• B. electrons occupy fixed energy levels and emit a photon when moving to a lower one
• C. the nucleus emits light directly
• D. electrons spiral into the nucleus

Explanation: Restricting electrons to discrete levels means only certain energy differences are available, so only certain frequencies appear, which is…

• A. n equals 1
• B. n equals 2
• C. n equals 3
• D. n equals 4

Explanation: Transitions to the second level release energies corresponding to visible light, which is why the Balmer lines are the ones seen through a…

• A. 6.63 times 10 to the minus 34 J s
• B. 3.0 times 10 to the 8 J s
• C. 1.6 times 10 to the minus 19 J s
• D. 9.1 times 10 to the minus 31 J s

Explanation: The extreme smallness of Planck's constant is why quantisation is invisible in everyday life and only matters at atomic scale.

• A. wavelength
• B. frequency
• C. speed
• D. amplitude

Explanation: Energy equals Planck's constant multiplied by frequency, so higher frequency means more energetic quanta, and since frequency and…

• A. cathode rays
• B. positive rays produced in a discharge tube with a perforated cathode
• C. radioactive decay of uranium
• D. the photoelectric effect

Explanation: Goldstein observed rays travelling towards the cathode and passing through holes in it, and the lightest positive particles, obtained when…

• A. positive rays are electromagnetic waves
• B. the positive ions formed are the ionised atoms of that particular gas
• C. positive rays travel faster
• D. the cathode is perforated

Explanation: Positive rays are the residue of atoms that have lost electrons, so their mass differs from gas to gas, whereas cathode rays are electrons…

• A. 0 only
• B. minus 1, 0 and plus 1
• C. minus 2 to plus 2
• D. plus 1 only

Explanation: The magnetic quantum number runs from minus l to plus l, and for a p subshell l equals 1, giving three values that correspond to the three…

• A. n equals 2, l equals 1, m equals 0
• B. n equals 3, l equals 2, m equals minus 2
• C. n equals 2, l equals 2, m equals 1
• D. n equals 1, l equals 0, m equals 0

Explanation: The azimuthal quantum number can never equal or exceed n, so l equal to 2 is impossible when n is 2, which would describe a non existent…

• A. their nuclei are unstable
• B. a half filled or completely filled d subshell is more stable
• C. they lose electrons easily
• D. the 4s orbital does not exist for them

Explanation: Promoting one 4s electron gives chromium a 3d5 4s1 arrangement and copper a 3d10 4s1 arrangement, both of which gain stability from the…

• A. electron affinity
• B. ionisation energy
• C. electronegativity
• D. lattice energy

Explanation: Ionisation energy is always endothermic because work must be done against the nuclear attraction, and it rises steeply for each successive…

• A. n=2, l=1, m=0, s=+1/2
• B. n=3, l=0, m=0, s=-1/2
• C. n=2, l=2, m=1, s=+1/2
• D. n=1, l=0, m=0, s=+1/2

Explanation: The azimuthal quantum number can only run from 0 up to n minus 1, so with n equal to 2 the value of l cannot reach 2, and the set…

• A. n
• B. l
• C. m
• D. s

Explanation: The azimuthal quantum number l fixes the subshell and therefore the shape, with l equal to 0 giving a spherical s orbital and l equal to 1…

• A. 6.6262x10-30 J.sec
• B. 6.6262x10-32 J.sec
• C. 6.6262x10+34 J.sec
• D. 6.6262x10-34 J.sec

Explanation: Planck's constant is 6.626 times 10 to the minus 34 joule seconds, and its extreme smallness is why quantisation is invisible in everyday…

• A. Three
• B. Four
• C. Five
• D. Six

Explanation: Neutral iron is [Ar] 3d6 4s2, and forming Fe3+ removes both 4s electrons and one 3d electron, leaving 3d5.

• A. 1
• B. 2
• C. 3
• D. 4

Explanation: Boron has atomic number 5, so its configuration is 1s2 2s2 2p1 and the single 2p electron is the only unpaired one.

• A. Electron
• B. Proton
• C. Neutron
• D. None of These

Explanation: The electron carries one negative elementary charge, while the proton carries an equal positive charge and the neutron has no charge.

• A. Shell
• B. Nucleus
• C. Energy levels
• D. Orbit

Explanation: The nucleus contains protons and neutrons, which account for almost all of an atom's mass; the electrons in the shells have extremely…

• A. Anode Rays
• B. Cathode Rays
• C. Canal Rays
• D. Gamma Rays

Explanation: Cathode rays are streams of electrons emitted from the cathode, so they carry negative charge.