ECAT — Engineering College Admission Test (UET)

ECAT Chemistry — Periodic Table, s- and p-Block Elements (Set 4)

Take the ECAT Chemistry — Periodic Table, s- and p-Block Elements (Set 4): 30 multiple-choice questions (40 minutes) with instant scoring and a full…

What this test covers

30 ECAT Chemistry

Sample questions with answers

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

Q1. Which of the elements Be, B, C and O has the lowest first ionization energy?
- A. Be
- B. O
- C. C
- D. B ✓
Answer: D. B
Explanation: First IEs (kJ mol⁻¹): Be 899, B 801, C 1086, O 1314. Boron is lower than Be because its outer electron is in a 2p orbital, which is higher in energy and better shielded than the filled 2s of Be.
Q2. Which of the following ions has the largest radius?
- A. O²⁻
- B. N³⁻ ✓
- C. F⁻
- D. Na⁺
Answer: B. N³⁻
Explanation: These are isoelectronic (10 electrons). The ion with the smallest nuclear charge holds the electrons least tightly: N³⁻ (Z = 7) is the largest.
Q3. The element with atomic number 33 belongs to which group and period?
- A. Group 15, period 3
- B. Group 15, period 4 ✓
- C. Group 13, period 4
- D. Group 17, period 4
Answer: B. Group 15, period 4
Explanation: Z = 33: [Ar] 3d¹⁰ 4s² 4p³. The valence shell is n = 4 (period 4) and it has 5 valence electrons (group 15). The element is arsenic.
Q4. What volume of H₂ at STP is obtained when 4.2 g of calcium hydride reacts with excess water? (CaH₂ + 2H₂O → Ca(OH)₂ + 2H₂; Ca = 40, H = 1)
- A. 1.12 L
- B. 8.96 L
- C. 4.48 L ✓
- D. 2.24 L
Answer: C. 4.48 L
Explanation: CaH₂ = 42 g mol⁻¹, so 4.2 g = 0.10 mol, which gives 0.20 mol H₂ = 0.20 × 22.4 = 4.48 L.
Q5. Potassium burns in excess air to form the superoxide KO₂. Which statement about KO₂ is correct?
- A. It is paramagnetic because the O₂⁻ ion has one unpaired electron ✓
- B. It is diamagnetic because O₂⁻ has all electrons paired
- C. It contains the O²⁻ ion and is colourless
- D. It is paramagnetic because it contains the O₂²⁻ ion
Answer: A. It is paramagnetic because the O₂⁻ ion has one unpaired electron
Explanation: The superoxide ion O₂⁻ has 17 electrons; in molecular orbital terms the last electron enters a π* orbital singly. KO₂ is therefore paramagnetic and yellow-orange.

The other 25 questions

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Q6. Which of the following is the correct order of solubility of the sulphates of group 2 metals in water?
- A. BaSO₄ > SrSO₄ > CaSO₄ > MgSO₄
- B. MgSO₄ = CaSO₄ > SrSO₄ > BaSO₄
- C. CaSO₄ > MgSO₄ > BaSO₄ > SrSO₄
- D. MgSO₄ > CaSO₄ > SrSO₄ > BaSO₄
Q7. Which of the following nitrates gives NO₂ gas, and not just oxygen, when heated?
- A. KNO₃
- B. LiNO₃
- C. NaNO₃
- D. RbNO₃
Q8. Gypsum (CaSO₄·2H₂O) loses water on heating at about 120 °C to give plaster of Paris (CaSO₄·½H₂O). What mass of plaster of Paris results from 17.2 g of gypsum? (Ca = 40, S = 32, O = 16, H = 1)
- A. 17.2 g
- B. 14.5 g
- C. 13.6 g
- D. 8.6 g
Q9. 0.015 mol of CO₂ is bubbled through limewater containing 0.010 mol of Ca(OH)₂. What mass of CaCO₃ remains as a precipitate at the end? (CaCO₃ = 100 g mol⁻¹; CaCO₃ + CO₂ + H₂O → Ca(HCO₃)₂)
- A. No precipitate remains
- B. 0.50 g
- C. 1.00 g
- D. 1.50 g
Q10. Boric acid, B(OH)₃, behaves as a weak monobasic acid in water because it
- A. accepts OH⁻ from water as a Lewis acid, releasing H⁺
- B. donates one of its three H atoms as H⁺ directly
- C. has one ionizable hydrogen bonded to boron
- D. dissociates into B³⁺ and 3OH⁻
Q11. What volume of H₂ at STP is produced when 2.7 g of aluminium reacts with excess aqueous NaOH? (2Al + 2NaOH + 6H₂O → 2Na[Al(OH)₄] + 3H₂; Al = 27)
- A. 3.36 L
- B. 2.24 L
- C. 6.72 L
- D. 4.48 L
Q12. PbO₂ is a strong oxidizing agent whereas SnO₂ is not. This is explained by
- A. the larger electronegativity of tin
- B. the inert pair effect, which makes Pb(II) more stable than Pb(IV)
- C. the absence of d orbitals in lead
- D. the lanthanide contraction making Sn⁴⁺ larger
Q13. The fullerene C₆₀ has a structure made of how many hexagonal faces?
- A. 12
- B. 60
- C. 30
- D. 20
Q14. In the Ostwald process all the nitrogen of 34 g NH₃ is converted overall to HNO₃ with an 80% overall yield. What mass of HNO₃ is obtained? (N = 14, H = 1, O = 16)
- A. 100.8 g
- B. 126 g
- C. 80.6 g
- D. 63 g
Q15. How many moles of NaOH are needed to completely neutralize one mole of phosphorous acid, H₃PO₃?
- A. 3
- B. 1
- C. 2
- D. 4
Q16. In the contact process SO₃ is absorbed in concentrated H₂SO₄ rather than water because
- A. absorption in water gives a fine acid mist and is violently exothermic; in H₂SO₄ it forms oleum (H₂S₂O₇)
- B. SO₃ is unreactive towards water, so it must be absorbed in concentrated H₂SO₄, where it simply dissolves as a gas
- C. concentrated H₂SO₄ acts as a better catalyst than V₂O₅ and so converts SO₃ to H₂SO₄ more rapidly
- D. SO₃ dissolves only in non-polar solvents, and concentrated H₂SO₄ behaves as a non-polar medium for it
Q17. Chlorine is passed through hot concentrated NaOH solution. The products are
- A. NaCl and NaClO
- B. NaClO and NaClO₃
- C. NaCl and NaClO₃
- D. NaClO₄ and NaCl
Q18. Bleaching powder is Ca(OCl)Cl (CaOCl₂, M = 127). If CaOCl₂ + 2HCl → CaCl₂ + H₂O + Cl₂, what is the maximum percentage of available chlorine in pure bleaching powder? (Cl = 35.5)
- A. 28%
- B. 71%
- C. 55.9%
- D. 27.9%
Q19. Which hydrogen halide is the strongest reducing agent?
- A. HCl
- B. HBr
- C. HI
- D. HF
Q20. XeF₆ is hydrolysed completely to give XeO₃. What are the shape and hybridization of XeO₃?
- A. Tetrahedral, sp³
- B. Trigonal planar, sp²
- C. T-shaped, sp³d
- D. Trigonal pyramidal, sp³
Q21. Which pair of elements shows a diagonal relationship in which both form amphoteric oxides?
- A. Li and Mg
- B. Na and Ca
- C. B and Si
- D. Be and Al
Q22. Temporary hardness is removed by Clark's method using lime: Ca(HCO₃)₂ + Ca(OH)₂ → 2CaCO₃ + 2H₂O. What mass of Ca(OH)₂ is needed per litre of water containing 162 mg of Ca(HCO₃)₂? (Ca(HCO₃)₂ = 162, Ca(OH)₂ = 74)
- A. 74 mg
- B. 162 mg
- C. 37 mg
- D. 148 mg
Q23. Both KO₂ and Na₂O₂ absorb CO₂ and release O₂ (4KO₂ + 2CO₂ → 2K₂CO₃ + 3O₂; 2Na₂O₂ + 2CO₂ → 2Na₂CO₃ + O₂). Per gram of solid, KO₂ releases about how many times as much O₂ as Na₂O₂? (K = 39, Na = 23, O = 16)
- A. 3.0
- B. 1.65
- C. 1.2
- D. 0.61
Q24. Magnesium metal is manufactured on a large scale by
- A. reduction of MgO with carbon in a blast furnace
- B. electrolysis of aqueous MgSO₄ solution
- C. electrolysis of molten MgCl₂ obtained from sea water
- D. heating MgCO₃ with sodium
Q25. Which period-3 oxide dissolves in both dilute HCl and aqueous NaOH?
- A. SiO₂
- B. MgO
- C. Al₂O₃
- D. P₄O₁₀
Q26. Successive ionization energies (kJ mol⁻¹) of an element are 578, 1817, 2745, 11577, 14842. In which group does it belong?
- A. Group 14
- B. Group 13
- C. Group 15
- D. Group 2
Q27. Gallium has almost the same atomic radius as aluminium despite being one period lower. The reason is
- A. poor shielding by the intervening 3d electrons
- B. the lanthanide contraction caused by the 4f electrons
- C. the inert pair effect of the 4s electrons in gallium
- D. the presence of 4f electrons in the gallium atom
Q28. Iodine is much more soluble in aqueous KI than in pure water because
- A. I₂ is oxidized by the iodide to form IO₃⁻ ions
- B. KI reacts with iodine to release hydrogen gas
- C. K⁺ forms covalent bonds with I₂ molecules
- D. I₂ combines with I⁻ to form the soluble I₃⁻ ion
Q29. '20 volume' hydrogen peroxide means 1 L of the solution gives 20 L of O₂ at STP on decomposition (2H₂O₂ → 2H₂O + O₂). What is its molarity? (molar volume 22.4 L)
- A. 1.79 M
- B. 20 M
- C. 3.58 M
- D. 0.89 M
Q30. CO₂ is a gas whereas SiO₂ is a hard solid. The main reason is that
- A. CO₂ is ionic while SiO₂ is covalent
- B. silicon cannot form single bonds with oxygen
- C. Si–O bonds are weaker than C–O bonds so SiO₂ is ionic
- D. carbon forms stable p–p π bonds, so CO₂ is made of discrete O=C=O molecules