ECAT — Engineering College Admission Test (UET)

ECAT Chemistry — Periodic Table, s- and p-Block Elements (Set 6)

Take the ECAT Chemistry — Periodic Table, s- and p-Block Elements (Set 6): 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. When lithium nitrate is strongly heated, it behaves like magnesium nitrate (and unlike sodium nitrate). The products are:
- A. Li₃N and O₂
- B. LiNO₂ and O₂
- C. LiO₂ and N₂
- D. Li₂O, NO₂ and O₂ ✓
Answer: D. Li₂O, NO₂ and O₂
Explanation: LiNO₃ decomposes as 4LiNO₃ → 2Li₂O + 4NO₂ + O₂, like Mg(NO₃)₂, a diagonal relationship. NaNO₃ gives NaNO₂ + O₂.
Q2. A salt imparts a crimson-red colour to a non-luminous Bunsen flame. The metal ion present is most likely:
- A. Ba²⁺
- B. Ca²⁺
- C. K⁺
- D. Sr²⁺ ✓
Answer: D. Sr²⁺
Explanation: Strontium gives a crimson flame; calcium is brick red, barium apple green and potassium lilac.
Q3. Among the sulphates MgSO₄, CaSO₄, SrSO₄ and BaSO₄, the one with the highest solubility in water is:
- A. CaSO₄
- B. SrSO₄
- C. BaSO₄
- D. MgSO₄ ✓
Answer: D. MgSO₄
Explanation: Solubility of Group 2 sulphates decreases down the group because the lattice energy falls less than the hydration energy; MgSO₄ dissolves readily while BaSO₄ is practically insoluble.
Q4. Which of these carbonates decomposes at the lowest temperature on heating?
- A. MgCO₃ ✓
- B. BaCO₃
- C. CaCO₃
- D. Na₂CO₃
Answer: A. MgCO₃
Explanation: The small, highly charged Mg²⁺ polarises the carbonate ion strongly, so MgCO₃ is the least thermally stable; Na₂CO₃ does not decompose on ordinary heating and stability rises down Group 2.
Q5. In Period 3 (Na to Ar) the first ionisation energy of an element is lower than that of the element immediately before it for:
- A. Si and Cl
- B. Na and Cl
- C. Al and S ✓
- D. Mg and P
Answer: C. Al and S
Explanation: Al (3p¹, outer electron shielded by 3s²) is lower than Mg; S (3p⁴, a paired electron with repulsion) is lower than P (half-filled 3p³).

The other 25 questions

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Q6. The successive ionisation energies (kJ mol⁻¹) of an element are 577, 1817, 2745, 11 577 and 14 842. The element belongs to group:
- A. 15
- B. 14
- C. 13
- D. 2
Q7. Which of these oxides is amphoteric?
- A. BeO
- B. CaO
- C. SrO
- D. MgO
Q8. Chlorine reacts with hot concentrated NaOH: 3Cl₂ + 6NaOH → 5NaCl + NaClO₃ + 3H₂O. The ratio of chlorine atoms reduced to those oxidised is:
- A. 3 : 1
- B. 5 : 1
- C. 1 : 5
- D. 1 : 1
Q9. Bleaching powder is represented by the formula Ca(OCl)Cl. The oxidation numbers of the two chlorine atoms are:
- A. +1 and −1
- B. +1 and +1
- C. −1 and −1
- D. +5 and −1
Q10. Complete hydrolysis of xenon hexafluoride, XeF₆ + 3H₂O → ?, gives the xenon compound:
- A. Xe(OH)₆
- B. XeOF₄
- C. XeO₂F₂
- D. XeO₃
Q11. The numbers of ionisable (acidic) hydrogen atoms in hypophosphorous acid H₃PO₂ and phosphorous acid H₃PO₃ are, respectively:
- A. 3 and 3
- B. 2 and 3
- C. 1 and 2
- D. 1 and 3
Q12. In the reaction 2H₂S + SO₂ → 3S + 2H₂O, the oxidising agent is:
- A. SO₂
- B. S
- C. H₂O
- D. H₂S
Q13. When oxalic acid is warmed with concentrated sulphuric acid, the gases evolved are:
- A. CO₂ only
- B. SO₂ and CO₂
- C. CO and CO₂
- D. CO and H₂
Q14. When solid NaI is warmed with concentrated sulphuric acid, which products are obtained?
- A. HI only
- B. I₂ and H₂S (with some SO₂)
- C. I₂ only, with H₂ gas
- D. SO₃ and HI
Q15. An aqueous solution of borax is alkaline because:
- A. the borate ion hydrolyses to give boric acid and hydroxide ions
- B. borax releases hydrogen ions on dissolving
- C. borax is a salt of a strong acid and a strong base
- D. borax contains free NaOH
Q16. Silicones are formed by hydrolysis and condensation of which of the following?
- A. (CH₃)₂SiCl₂
- B. SiCl₄
- C. (CH₃)₃SiCl alone
- D. CH₃SiH₃
Q17. 2.7 g of aluminium is dissolved in excess aqueous NaOH: 2Al + 2NaOH + 6H₂O → 2Na[Al(OH)₄] + 3H₂ (Al = 27). The volume of H₂ liberated at STP (22.4 dm³ mol⁻¹) is:
- A. 6.72 dm³
- B. 3.36 dm³
- C. 4.48 dm³
- D. 2.24 dm³
Q18. In the thermite reaction Fe₂O₃ + 2Al → Al₂O₃ + 2Fe (Fe = 56, Al = 27), the mass of iron obtained from 27 g of aluminium is:
- A. 112 g
- B. 84 g
- C. 28 g
- D. 56 g
Q19. Potassium burns in excess oxygen to give the superoxide KO₂. The oxidation number of oxygen in KO₂ is:
- A. +1/2
- B. −1
- C. −1/2
- D. −2
Q20. 168 g of sodium hydrogencarbonate is heated strongly: 2NaHCO₃ → Na₂CO₃ + CO₂ + H₂O (Na = 23, H = 1, C = 12, O = 16). The loss in mass is:
- A. 62 g
- B. 18 g
- C. 106 g
- D. 44 g
Q21. Calcium hydride reacts with water: CaH₂ + 2H₂O → Ca(OH)₂ + 2H₂ (Ca = 40, H = 1). The mass of CaH₂ needed to produce 1.0 mol of H₂ is:
- A. 42 g
- B. 84 g
- C. 10.5 g
- D. 21 g
Q22. 0.10 mol of magnesium nitride is treated with excess water: Mg₃N₂ + 6H₂O → 3Mg(OH)₂ + 2NH₃. The amount of ammonia produced is:
- A. 0.60 mol
- B. 0.30 mol
- C. 0.20 mol
- D. 0.10 mol
Q23. Which of the following elements has the highest second ionisation energy?
- A. Si
- B. Na
- C. Mg
- D. Al
Q24. White phosphorus reacts with hot aqueous NaOH to give a poisonous gas, which is:
- A. NH₃
- B. PH₃
- C. H₂S
- D. P₂O₅
Q25. Which halogen shows no positive oxidation state in its compounds?
- A. chlorine
- B. bromine
- C. iodine
- D. fluorine
Q26. Bartlett prepared the first noble gas compound, XePtF₆, after noticing that O₂ reacts with PtF₆ to form O₂⁺PtF₆⁻. His reasoning was that:
- A. xenon forms a covalent bond with oxygen easily, so Xe could replace O₂ in the salt
- B. PtF₆ is such a strong fluorinating agent that it can oxidise only noble gases
- C. xenon is chemically more reactive than molecular oxygen towards fluorine compounds
- D. the first ionisation energy of Xe is almost the same as that of O₂
Q27. In the layers of graphite, each carbon atom is bonded to how many neighbouring carbon atoms and what is its hybridisation?
- A. four, sp³
- B. four, sp²
- C. three, sp²
- D. three, sp³
Q28. Ordinary hydrogen gas at room temperature is a mixture of ortho and para forms in the ratio ortho : para equal to:
- A. 1 : 3 (ortho : para)
- B. 9 : 1 (ortho : para)
- C. 3 : 1 (ortho : para)
- D. 1 : 1 (ortho : para)
Q29. In water, which hydride is the strongest acid?
- A. They are equally strong
- B. H₂S
- C. H₂Se
- D. H₂O
Q30. The compound SnCl₂ is a good reducing agent, whereas PbO₂ is a strong oxidising agent. This is best explained by:
- A. the inert pair effect, favouring +2 over +4 in heavier members
- B. the higher electronegativity of lead compared with tin
- C. the complete absence of d electrons in the lead atom
- D. the larger size of tin, which makes the +4 state more stable