NUMS — Medical & Dental Entry Test

NUMS Chemistry — Fundamental Concepts, Atomic Structure and Bonding (Set 3)

Take the NUMS Chemistry — Fundamental Concepts, Atomic Structure and Bonding (Set 3): 30 multiple-choice questions (40 minutes) with instant scoring and a…

What this test covers

30 NUMS Chemistry

Sample questions with answers

The first 5 questions of this test, with the correct answer and explanation.

Q1. Anhydrous CuSO₄ combines with five molecules of water of crystallisation to form CuSO₄·5H₂O. What is the percentage of water by mass in the hydrate? (Cu = 63.5, S = 32, O = 16, H = 1)
- A. 18.0%
- B. 63.9%
- C. 28.6%
- D. 36.1% ✓
Answer: D. 36.1%
Explanation: Molar mass of CuSO₄·5H₂O = 159.5 + 90 = 249.5 g/mol; water = 90/249.5 × 100 = 36.1%.
Q2. 50 mL of a 2.0 M NaOH solution is diluted with water to a final volume of 250 mL. What is the molarity of the diluted solution?
- A. 0.50 M
- B. 0.40 M ✓
- C. 0.10 M
- D. 0.25 M
Answer: B. 0.40 M
Explanation: M₁V₁ = M₂V₂ gives M₂ = (2.0 × 50)/250 = 0.40 M.
Q3. How many ions are present in 0.10 mole of CaCl₂ when it is completely dissociated? (Nₐ = 6.02 × 10²³)
- A. 1.81 × 10²³ ✓
- B. 3.01 × 10²³
- C. 6.02 × 10²²
- D. 1.20 × 10²³
Answer: A. 1.81 × 10²³
Explanation: Each formula unit gives 1 Ca²⁺ + 2 Cl⁻ = 3 ions; 0.10 × 3 × 6.02 × 10²³ = 1.81 × 10²³.
Q4. Combustion of 0.46 g of an organic compound containing only C, H and O gives 0.88 g of CO₂ and 0.54 g of H₂O. What is its empirical formula?
- A. CH₃O
- B. CH₂O
- C. C₂H₄O
- D. C₂H₆O ✓
Answer: D. C₂H₆O
Explanation: C = 0.88 × 12/44 = 0.24 g; H = 0.54 × 2/18 = 0.06 g; O = 0.46 − 0.30 = 0.16 g. Moles: C 0.02, H 0.06, O 0.01, ratio 2 : 6 : 1.
Q5. A hydrocarbon has the empirical formula CH and a vapour density of 39. What is its molecular formula?
- A. C₄H₄
- B. C₆H₆ ✓
- C. C₂H₂
- D. C₃H₃
Answer: B. C₆H₆
Explanation: Molar mass = 2 × vapour density = 78. Empirical mass 13, so n = 6 and the formula is C₆H₆.

The other 25 questions

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Q6. Which ion is isoelectronic with the chloride ion, Cl⁻?
- A. Na⁺
- B. K⁺
- C. Mg²⁺
- D. F⁻
Q7. In Rutherford's gold-foil experiment a very small fraction of α-particles were deflected through angles greater than 90°. What did this show?
- A. The positive charge and most of the mass are concentrated in a tiny nucleus
- B. Electrons are embedded uniformly in a positive sphere
- C. Alpha particles are heavier than gold atoms
- D. Atoms have electrons orbiting in fixed energy levels
Q8. Moseley's study of the X-ray spectra of elements showed that the square root of the X-ray frequency is proportional to which quantity?
- A. Number of neutrons
- B. Atomic number
- C. Atomic mass
- D. Electronegativity
Q9. How many orbitals are present in the third principal energy level (n = 3)?
- A. 9
- B. 6
- C. 3
- D. 18
Q10. How many nodes in total (radial plus angular) does a 4d orbital have?
- A. 1
- B. 4
- C. 2
- D. 3
Q11. How many unpaired electrons are present in a chromium atom (Z = 24) in its ground state?
- A. 4
- B. 2
- C. 6
- D. 5
Q12. What is the spin-only magnetic moment of the Fe³⁺ ion (Z = 26) in Bohr magnetons?
- A. 2.83 BM
- B. 5.92 BM
- C. 3.87 BM
- D. 4.90 BM
Q13. According to Bohr's model, what is the radius of the third orbit of hydrogen? (a₀ = 0.529 Å)
- A. 1.59 Å
- B. 2.12 Å
- C. 14.28 Å
- D. 4.76 Å
Q14. What is the ground-state energy of the electron in Li²⁺ (Z = 3)? (Eₙ = −13.6 Z²/n² eV)
- A. −30.6 eV
- B. −122.4 eV
- C. −40.8 eV
- D. −13.6 eV
Q15. What is the wavelength of the longest-wavelength line in the Balmer series of hydrogen? (R = 1.097 × 10⁷ m⁻¹)
- A. 656 nm
- B. 122 nm
- C. 486 nm
- D. 365 nm
Q16. What is the energy of a photon of wavelength 500 nm? (h = 6.626 × 10⁻³⁴ J s, c = 3.0 × 10⁸ m/s)
- A. 7.95 × 10⁻¹⁹ J
- B. 39.8 × 10⁻¹⁹ J
- C. 1.99 × 10⁻¹⁹ J
- D. 3.98 × 10⁻¹⁹ J
Q17. Which of the diatomic molecules B₂, C₂, N₂ and F₂ is paramagnetic in its ground state?
- A. B₂
- B. F₂
- C. C₂
- D. N₂
Q18. What is the shape of the SF₄ molecule?
- A. See-saw
- B. Tetrahedral
- C. Square planar
- D. Trigonal bipyramidal
Q19. What are the shape and hybridisation of the XeF₂ molecule?
- A. Bent, sp³
- B. Linear, sp³d
- C. Trigonal planar, sp²
- D. Linear, sp
Q20. What is the shape of the ICl₄⁻ ion?
- A. See-saw
- B. Square planar
- C. Tetrahedral
- D. Square pyramidal
Q21. In the Lewis structure of the carbonate ion drawn with one C=O and two C–O single bonds, what is the formal charge on each singly bonded oxygen?
- A. 0
- B. −1
- C. −2
- D. +1
Q22. Why is the H–O–H bond angle in water (104.5°) smaller than the H–N–H angle in ammonia (107°)?
- A. Water has two lone pairs, which repel bonding pairs more than one lone pair does
- B. Oxygen is less electronegative than nitrogen
- C. Oxygen uses pure p orbitals while nitrogen uses sp³ hybrids
- D. Water forms hydrogen bonds but ammonia does not
Q23. Which of the hydrogen halides HF, HCl, HBr and HI has the second-highest boiling point?
- A. HF
- B. HI
- C. HCl
- D. HBr
Q24. Fluorine is a gas at room temperature but iodine is a solid. What is the main reason?
- A. Iodine molecules are ionic in the solid state
- B. Iodine molecules form hydrogen bonds between them
- C. The I–I bond is stronger than the F–F bond
- D. Larger iodine molecules have stronger London dispersion forces
Q25. Which of the following molecules has polar bonds but a zero net dipole moment?
- A. SO₂
- B. NH₃
- C. CHCl₃
- D. CCl₄
Q26. What is the hybridisation of the central carbon atom in allene, CH₂=C=CH₂?
- A. sp³
- B. sp³d
- C. sp²
- D. sp
Q27. How many σ and π bonds are present in a molecule of propyne, CH₃–C≡CH?
- A. 6 σ and 2 π
- B. 7 σ and 1 π
- C. 6 σ and 3 π
- D. 5 σ and 3 π
Q28. 10.0 g of CaCO₃ is heated and gives 3.96 g of CO₂ (CaCO₃ → CaO + CO₂). What is the percentage yield of CO₂? (Ca = 40, C = 12, O = 16)
- A. 90%
- B. 80%
- C. 95%
- D. 85%
Q29. How many electrons are present in 1.8 g of water? (H₂O = 18 g/mol, Nₐ = 6.02 × 10²³)
- A. 6.02 × 10²³
- B. 3.01 × 10²³
- C. 6.02 × 10²²
- D. 1.20 × 10²⁴
Q30. Why is the radius of Fe³⁺ smaller than that of Fe²⁺?
- A. Fe³⁺ gains an extra inner shell of electrons
- B. Fe³⁺ has more protons in its nucleus than Fe²⁺
- C. Fe³⁺ has lost a complete shell of electrons
- D. The same nuclear charge holds fewer electrons more tightly