Practice Atomic Structure MCQs for BSN Nursing Entry Test Chemistry — topic-wise sets with solved answers.
Q1. During a discharge tube experiment, high-velocity cathode rays strike the glass walls of the tube. What is the observable result of this specific interaction?
Answer: Produce a greenish fluorescence
Explanation: Cathode rays produce fluorescence when striking glass; X-rays are only produced when these rays hit heavy metal targets like tungsten.
Q2. In the ionization chamber of a mass spectrometer, what mechanism is utilized to convert vaporized atoms into positive ions before acceleration?
Answer: Electron bombardment
Explanation: High-energy electrons knock out valence electrons from vaporized atoms to form positive ions; thermal ionization is used for different applications.
Q3. A researcher attempts to determine the exact trajectory of an electron within an atom. Which pair of variables is fundamentally impossible to measure simultaneously?
Answer: Position and momentum
Explanation: Heisenberg's principle states position and momentum cannot be measured simultaneously; Bohr's model fails because it assumes fixed paths for electrons.
Q4. In the production of characteristic X-rays, a K-alpha photon is emitted when an electron transition occurs between which two specific energy levels?
Answer: L-shell to K-shell
Explanation: K-alpha X-rays occur when an L-shell electron fills a K-shell vacancy; K-beta transitions involve M-shell electrons falling to the K-shell.
Q5. A student needs to calculate the total number of orbitals available in the M-shell (n=3). Which formula correctly determines this value?
Answer: n^2
Explanation: The formula n-squared gives the total orbitals in a shell; 2n-squared calculates the maximum number of electrons instead.
Q6. Considering the extra stability of half-filled subshells, what is the ground state electronic configuration of a Chromium (Z=24) atom?
Answer: [Ar] 4s1 3d5
Explanation: Chromium adopts a 4s1 3d5 configuration for extra stability; 4s2 3d4 is the expected but incorrect ground state configuration.
Q7. In a mass spectrometer, if an operator wishes to increase the radius of the circular path for a specific ion, which adjustment should be made?
Answer: Decrease the magnetic field strength
Explanation: Decreasing the magnetic field H increases the radius r, as m/e equals (H^2 r^2) / 2E; increasing E would decrease r.
Q8. The Davisson-Germer experiment confirmed the de Broglie hypothesis by demonstrating which wave-like behavior of electrons when striking a nickel crystal?
Answer: Diffraction by crystals
Explanation: Diffraction is a wave property; the photoelectric effect and blackbody radiation demonstrate the particle nature of electromagnetic radiation.
Q9. During the discharge of hydrogen gas, visible light is emitted. To which principal energy level must the electrons fall to produce these specific spectral lines?
Answer: n=2
Explanation: The Balmer series results from transitions to n=2; Lyman series involves transitions to n=1, producing ultraviolet radiation.
Q10. When an atom is placed in an external magnetic field, the magnetic quantum number 'm' specifically describes which property of the electron's orbital?
Answer: Orientation of the orbital
Explanation: The magnetic quantum number (m) describes orbital orientation; the azimuthal quantum number (l) determines the shape of the orbital.
Q11. The energy of an electron in any orbit of a hydrogen atom is always negative. What is the physical significance of this negative sign?
Answer: Work must be done to remove it
Explanation: Energy is zero at infinity; as the electron approaches the nucleus, energy decreases below zero, making it more negative.
Q12. Unlike cathode rays, the nature of positive rays (canal rays) depends on the gas used in the tube. How are these rays primarily produced?
Answer: Ionization of residual gas
Explanation: Positive rays are formed from residual gas molecules after electron impact; they do not originate directly from the anode material.
Q13. An orbital can hold a maximum of two electrons with opposite spins. Which principle or rule is specifically defined by this requirement?
Answer: Pauli Exclusion Principle
Explanation: The Pauli Exclusion Principle requires electrons in the same orbital to have opposite spins; Hund's Rule deals with degenerate orbitals.
Q14. Moseley's study of X-ray frequencies revealed that the square root of the frequency is directly proportional to which property of the target metal?
Answer: Atomic number
Explanation: Moseley showed frequency depends on atomic number (Z); atomic mass (A) was previously thought to be the fundamental property.
Q15. If the radius of the first Bohr orbit of hydrogen is 0.529 Angstrom, what is the calculated radius of the second orbit (n=2)?
Answer: 2.116 Angstrom
Explanation: The radius of the nth orbit is proportional to n-squared; doubling n from 1 to 2 increases the radius four times.
Q16. Which quantum number is responsible for dividing the main shell into subshells and determining the geometric shape of the orbitals?
Answer: Azimuthal quantum number
Explanation: The azimuthal quantum number 'l' defines subshell shape (s, p, d, f); 'n' defines the main energy level or shell size.
Q17. What is the correct electronic configuration for Copper (Z=29), accounting for the stability associated with a completely filled d-subshell?
Answer: [Ar] 4s1 3d10
Explanation: Copper achieves a full 3d subshell (3d10) for stability; 4s2 3d9 is the predicted but less stable configuration.
Q18. In a discharge tube, the velocity of the produced cathode rays is primarily dependent on which of the following experimental parameters?
Answer: The potential difference applied
Explanation: Voltage determines the energy/velocity of cathode rays; the nature of the cathode material does not change the ray properties.
Q19. When an electron in a hydrogen atom jumps from higher orbits to the first orbit (n=1), which spectral series is produced?
Answer: Lyman series
Explanation: The Lyman series is found in the UV region; Balmer is in the visible region and Paschen is in the infrared.
Q20. A scientist observes the splitting of spectral lines when a hydrogen discharge tube is placed in a strong magnetic field. What is this phenomenon called?
Answer: Zeeman effect
Explanation: The Zeeman effect is the splitting of lines in a magnetic field; the Stark effect refers to splitting in an electric field.
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