NUMS — Medical & Dental Entry Test

NUMS Chemistry — Fundamental Concepts, Atomic Structure and Bonding (Set 2)

Take the NUMS Chemistry — Fundamental Concepts, Atomic Structure and Bonding (Set 2): 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. A mixture of 4 g of hydrogen gas and 16 g of oxygen gas is exploded to form water (2H₂ + O₂ → 2H₂O). What mass of water is formed?
- A. 20 g
- B. 9 g
- C. 36 g
- D. 18 g ✓
Answer: D. 18 g
Explanation: H₂ = 4/2 = 2 mol, O₂ = 16/32 = 0.5 mol. 2 mol H₂ would need 1 mol O₂, so O₂ is limiting; 0.5 mol O₂ gives 1 mol H₂O = 18 g.
Q2. A sugar found in fruit contains 40.0% C, 6.7% H and 53.3% O by mass and has a molar mass of 180 g mol⁻¹. What is its molecular formula?
- A. C₆H₁₂O₆ ✓
- B. CH₂O
- C. C₃H₆O₃
- D. C₆H₆O₆
Answer: A. C₆H₁₂O₆
Explanation: Mole ratio C : H : O = 40/12 : 6.7/1 : 53.3/16 = 3.33 : 6.7 : 3.33 = 1 : 2 : 1, so the empirical formula is CH₂O (30). 180/30 = 6, giving C₆H₁₂O₆.
Q3. A patient drinks 9 g of water. How many water molecules is this? (Nₐ = 6.02 × 10²³ mol⁻¹, H₂O = 18 g mol⁻¹)
- A. 6.02 × 10²³
- B. 3.01 × 10²³ ✓
- C. 5.42 × 10²⁴
- D. 1.20 × 10²⁴
Answer: B. 3.01 × 10²³
Explanation: Moles = 9/18 = 0.5 mol; molecules = 0.5 × 6.02 × 10²³ = 3.01 × 10²³.
Q4. What is the mass of a single carbon-12 atom? (Nₐ = 6.022 × 10²³ mol⁻¹)
- A. 1.99 × 10⁻²² g
- B. 1.99 × 10⁻²³ g ✓
- C. 7.23 × 10²⁴ g
- D. 1.66 × 10⁻²⁴ g
Answer: B. 1.99 × 10⁻²³ g
Explanation: One mole (12 g) contains Nₐ atoms, so one atom has mass 12/(6.022 × 10²³) = 1.99e-23 g.
Q5. Natural gas (methane) burns according to CH₄ + 2O₂ → CO₂ + 2H₂O. What volume of oxygen, measured at STP, is needed to burn 8 g of methane completely?
- A. 11.2 dm³
- B. 5.6 dm³
- C. 44.8 dm³
- D. 22.4 dm³ ✓
Answer: D. 22.4 dm³
Explanation: 8 g CH₄ = 8/16 = 0.5 mol, which needs 2 × 0.5 = 1 mol O₂; at STP 1 mol occupies 22.4 dm³.

The other 25 questions

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Q6. Limestone decomposes on heating: CaCO₃ → CaO + CO₂. What mass of carbon dioxide is released when 10 g of CaCO₃ (M = 100 g mol⁻¹) decomposes completely?
- A. 5.6 g
- B. 4.4 g
- C. 10 g
- D. 2.2 g
Q7. How many moles of atoms in total are present in 0.1 mol of sulphuric acid, H₂SO₄?
- A. 0.1 mol
- B. 7 mol
- C. 0.7 mol
- D. 0.4 mol
Q8. What is the maximum number of electrons that can have the quantum numbers n = 4 and l = 1?
- A. 10
- B. 2
- C. 32
- D. 6
Q9. How many orbitals are present in a subshell with azimuthal quantum number l = 3?
- A. 5
- B. 7
- C. 3
- D. 14
Q10. According to the (n + l) rule, which of these orbitals is filled first?
- A. 4p
- B. 4d
- C. 5s
- D. 3d
Q11. Chromium (Z = 24) is a trace element needed for glucose metabolism. What is the ground-state electronic configuration of a chromium atom?
- A. [Ar] 3d⁵ 4s¹
- B. [Ar] 3d³ 4s² 4p¹
- C. [Ar] 3d⁴ 4s²
- D. [Ar] 3d⁶
Q12. The red line of the hydrogen spectrum arises from the transition n = 3 → n = 2. Using the Rydberg constant R = 1.097 × 10⁷ m⁻¹, what is its wavelength?
- A. 486 nm
- B. 656 nm
- C. 122 nm
- D. 1875 nm
Q13. The radius of the first Bohr orbit of hydrogen is 0.529 Å. What is the radius of the third orbit?
- A. 4.76 Å
- B. 2.12 Å
- C. 1.59 Å
- D. 0.176 Å
Q14. Why is the de Broglie wavelength of a 0.1 kg cricket ball moving at 10 m s⁻¹ never noticed in daily life? (h = 6.63 × 10⁻³⁴ J s)
- A. λ = 6.63 × 10⁻³⁵ m, but the ball has no wave nature
- B. λ = 6.63 × 10⁻³³ m, comparable to light waves
- C. λ = 6.63 × 10⁻³⁴ m, far too small to detect
- D. λ = 6.63 × 10⁻³² m, comparable to atomic size
Q15. In discharge-tube experiments the charge-to-mass ratio (e/m) of cathode-ray particles was found to be the same whatever gas or electrode metal was used. What did this show?
- A. Electrons are a common constituent of all atoms
- B. Cathode rays are electromagnetic waves
- C. The gas atoms carry a positive charge
- D. The nucleus contains neutrons
Q16. In Rutherford's gold-foil experiment, most alpha particles passed straight through the foil. What conclusion was drawn from this observation?
- A. Most of the atom is empty space
- B. Alpha particles have very little mass
- C. Electrons revolve in fixed orbits
- D. The nucleus is negatively charged
Q17. The first ionisation energy of aluminium (Z = 13) is lower than that of magnesium (Z = 12). What is the reason?
- A. Aluminium atoms are smaller than magnesium atoms
- B. The 3s subshell of aluminium is half-filled
- C. Aluminium has a smaller nuclear charge than magnesium
- D. The electron removed from Al is a 3p electron, which is higher in energy and shielded by 3s electrons
Q18. Fluorine is the most electronegative element, yet chlorine has a more negative (higher) electron affinity. Why?
- A. Chlorine forms ionic bonds more easily than fluorine
- B. Fluorine's small size causes strong repulsion between the added electron and existing electrons
- C. Chlorine has a lower nuclear charge than fluorine
- D. Fluorine already has a completely filled valence shell
Q19. What are the hybridisation of boron and the shape of the boron trifluoride (BF₃) molecule?
- A. sp³, tetrahedral
- B. sp³, trigonal pyramidal
- C. sp, linear
- D. sp², trigonal planar
Q20. Phosphorus pentachloride (PCl₅) in the gas phase has five P–Cl bond pairs and no lone pair on phosphorus. What is its geometry?
- A. Square pyramidal
- B. Octahedral
- C. Square planar
- D. Trigonal bipyramidal
Q21. In which of the following species is a coordinate covalent (dative) bond present?
- A. NaCl
- B. NH₄⁺
- C. CH₄
- D. H₂O
Q22. Nitrogen gas can be ionised in a discharge to N₂⁺. Using molecular orbital theory, what bond order does the N₂⁺ ion have?
- A. 2
- B. 3
- C. 2.5
- D. 3.5
Q23. Which of the following molecules has a net dipole moment?
- A. NH₃
- B. CO₂
- C. CH₄
- D. BF₃
Q24. Methane, ammonia and water all have sp³-hybridised central atoms. How do their H–X–H bond angles compare?
- A. NH₃ > CH₄ > H₂O
- B. H₂O > NH₃ > CH₄
- C. CH₄ > NH₃ > H₂O
- D. CH₄ = NH₃ = H₂O
Q25. Which chloride shows the greatest covalent character?
- A. MgCl₂
- B. AlCl₃
- C. KCl
- D. NaCl
Q26. o-Nitrophenol is steam-volatile and boils at a lower temperature than p-nitrophenol. What explains this?
- A. p-Nitrophenol cannot form hydrogen bonds at all
- B. o-Nitrophenol forms intramolecular hydrogen bonds, while p-nitrophenol forms intermolecular hydrogen bonds
- C. o-Nitrophenol has a higher molar mass than p-nitrophenol
- D. o-Nitrophenol is ionic while p-nitrophenol is covalent
Q27. Which ranking of carbon–carbon bond lengths is correct?
- A. C≡C > C=C > C–C
- B. C=C > C–C > C≡C
- C. C–C = C=C = C≡C
- D. C–C > C=C > C≡C
Q28. 50 cm³ of 2.0 M hydrochloric acid is diluted with water to a total volume of 500 cm³. What is the molarity of the diluted acid?
- A. 20 M
- B. 0.20 M
- C. 0.40 M
- D. 0.10 M
Q29. What is the mass of 5.6 dm³ of carbon dioxide gas measured at STP?
- A. 11 g
- B. 5.5 g
- C. 22 g
- D. 44 g
Q30. In a mass spectrometer, positive ions with the same speed pass through the same magnetic field. Which ions are deflected the most?
- A. Neutral atoms of the lightest isotope
- B. Ions with the largest mass-to-charge ratio (m/e)
- C. Ions with the smallest mass-to-charge ratio (m/e)
- D. All ions are deflected equally