ECAT — Engineering College Admission Test (UET)

ECAT Chemistry — Periodic Table, s- and p-Block Elements (Set 3)

Take the ECAT Chemistry — Periodic Table, s- and p-Block Elements (Set 3): 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. Using Slater's rules, the effective nuclear charge felt by the 3s electron of sodium (Z = 11) is:
- A. 2.2 ✓
- B. 8.8
- C. 1.0
- D. 10.0
Answer: A. 2.2
Explanation: Shielding = 8 × 0.85 (n−1 shell) + 2 × 1.00 (n−2 shell) = 8.8; Z* = 11 − 8.8 = 2.2.
Q2. The correct order of radii of the isoelectronic species O²⁻, F⁻, Na⁺ and Mg²⁺ is:
- A. F⁻ > O²⁻ > Na⁺ > Mg²⁺
- B. O²⁻ > F⁻ > Na⁺ > Mg²⁺ ✓
- C. O²⁻ > Na⁺ > F⁻ > Mg²⁺
- D. Mg²⁺ > Na⁺ > F⁻ > O²⁻
Answer: B. O²⁻ > F⁻ > Na⁺ > Mg²⁺
Explanation: With the same 10 electrons, the greater the nuclear charge the stronger the pull and the smaller the radius.
Q3. Which of the following has the highest electron affinity (most negative value)?
- A. Oxygen
- B. Chlorine ✓
- C. Bromine
- D. Fluorine
Answer: B. Chlorine
Explanation: F has a smaller value than Cl because added electron repels the compact 2p electrons; Cl has the highest electron affinity in the periodic table.
Q4. Which oxide of a period-3 element gives the strongest acid on dissolving in water?
- A. SO₃
- B. P₄O₁₀
- C. Cl₂O₇ ✓
- D. SiO₂
Answer: C. Cl₂O₇
Explanation: Cl₂O₇ + H₂O → 2HClO₄; acidity of oxides rises across the period.
Q5. Sodium peroxide reacts with cold water to give:
- A. Na₂O and O₂
- B. NaH and O₂
- C. NaOH and O₂
- D. NaOH and H₂O₂ ✓
Answer: D. NaOH and H₂O₂
Explanation: Na₂O₂ + 2H₂O → 2NaOH + H₂O₂ (the peroxide ion is hydrolysed).

The other 25 questions

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Q6. Potassium superoxide (KO₂) is used in breathing apparatus because it:
- A. absorbs O₂ and releases CO₂
- B. releases only H₂
- C. absorbs CO₂ and releases O₂
- D. absorbs nitrogen
Q7. Which alkali metal burns in nitrogen at room temperature to give a nitride?
- A. Sodium
- B. Lithium
- C. Potassium
- D. Caesium
Q8. The colour imparted to a flame by calcium and barium compounds is respectively:
- A. golden yellow and violet
- B. brick red and apple green
- C. crimson and brick red
- D. apple green and brick red
Q9. In the Solvay process the compound that separates from the ammoniacal brine as a precipitate is:
- A. NaHCO₃
- B. Na₂CO₃
- C. CaCO₃
- D. NaCl
Q10. How much quicklime (CaO) is obtained by heating 1000 kg of pure CaCO₃? (Ca = 40, C = 12, O = 16)
- A. 560 kg
- B. 280 kg
- C. 440 kg
- D. 1000 kg
Q11. Plaster of Paris and gypsum have the formulas respectively:
- A. CaSO₄·½H₂O and CaSO₄·2H₂O
- B. CaSO₄·5H₂O and CaSO₄·½H₂O
- C. CaSO₄·2H₂O and CaSO₄·½H₂O
- D. CaSO₄ and CaSO₄·H₂O
Q12. Magnesium burns in air to give mainly MgO, but a small amount of another compound also forms. It is:
- A. Mg₃N₂
- B. MgH₂
- C. MgO₂
- D. Mg(OH)₂
Q13. The Lewis acidity of BF₃ is explained by:
- A. hydrogen bonding in BF₃
- B. the sp³ hybridisation of boron
- C. the empty 2p orbital on boron, which can accept a lone pair
- D. the lone pair on boron
Q14. Boric acid, B(OH)₃, in water behaves as:
- A. a Brønsted base
- B. a weak monobasic Lewis acid
- C. a strong dibasic Brønsted acid
- D. a tribasic Brønsted acid
Q15. The structure of diborane (B₂H₆) contains:
- A. two three-centre, two-electron (banana) bridge bonds
- B. a B≡B triple bond
- C. only terminal two-centre bonds
- D. two ionic B–H bonds
Q16. Aluminium dissolves in aqueous NaOH to give:
- A. Al₂O₃ and H₂
- B. NaAlO₂ and O₂
- C. sodium tetrahydroxoaluminate and hydrogen
- D. no reaction takes place
Q17. The inert pair effect explains that:
- A. C(II) is more stable than C(IV)
- B. Si(II) is the common oxidation state
- C. Pb(IV) is more stable than Pb(II)
- D. Pb(II) is more stable than Pb(IV)
Q18. CCl₄ is not hydrolysed by water whereas SiCl₄ is readily hydrolysed because:
- A. silicon has vacant 3d orbitals to accept the lone pair of water
- B. C–Cl bond is stronger than Si–Cl bond only
- C. SiCl₄ is ionic
- D. CCl₄ is soluble in water
Q19. Carbon dioxide is a gas while silicon dioxide is a high-melting solid because:
- A. SiO₂ is an ionic solid like NaCl
- B. SiO₂ forms a giant covalent network, while CO₂ has discrete molecules
- C. CO₂ forms strong hydrogen bonds between its molecules
- D. Si is much more electronegative than C
Q20. Which is the correct order of basic character of the hydrides NH₃, PH₃, AsH₃?
- A. NH₃ > PH₃ > AsH₃
- B. AsH₃ > PH₃ > NH₃
- C. NH₃ > AsH₃ > PH₃
- D. PH₃ > NH₃ > AsH₃
Q21. Copper reacts with dilute and with concentrated nitric acid to give respectively:
- A. NO₂ and NO
- B. H₂ and NO₂
- C. N₂O and NO
- D. NO and NO₂
Q22. In the Ostwald process, ammonia is catalytically oxidised to:
- A. nitrous oxide
- B. nitric oxide (NO)
- C. nitrogen dioxide directly
- D. nitrogen
Q23. The basicity (number of ionisable H atoms) of phosphorous acid, H₃PO₃, and hypophosphorous acid, H₃PO₂, are respectively:
- A. 1 and 1
- B. 3 and 2
- C. 2 and 1
- D. 3 and 3
Q24. Compared with white phosphorus, red phosphorus is:
- A. more reactive and soluble in CS₂
- B. made of discrete P₄ molecules
- C. less reactive and insoluble in CS₂
- D. poisonous and glows in the dark
Q25. In the contact process for sulphuric acid, SO₃ is absorbed in concentrated H₂SO₄ rather than water because:
- A. H₂SO₄ is made only as an oleum
- B. SO₃ does not dissolve in water
- C. water reacts with V₂O₅
- D. direct absorption in water forms a corrosive acid mist that is hard to condense
Q26. Which halogen displaces bromine from an aqueous solution of KBr?
- A. Astatine
- B. Neon
- C. Chlorine
- D. Iodine
Q27. Among the oxoacids of chlorine, the strongest acid is:
- A. HClO₄
- B. HClO₃
- C. HClO
- D. HClO₂
Q28. Bleaching powder is obtained by passing chlorine over:
- A. quicklime CaO
- B. limestone CaCO₃
- C. caustic soda
- D. dry slaked lime Ca(OH)₂
Q29. Which noble gas has the lowest boiling point and so is used for cooling in cryogenics?
- A. Argon
- B. Helium
- C. Xenon
- D. Neon
Q30. Which of the following hydrides is ionic and gives hydrogen with water?
- A. PdH₀.₆
- B. HCl
- C. CH₄
- D. NaH