ECAT — Engineering College Admission Test (UET)
Take the ECAT Chemistry — Periodic Table, s- and p-Block Elements (Set 7): 30 multiple-choice questions (40 minutes) with instant scoring and a full…
What this test covers
The first 5 questions of this test, with the correct answer and explanation.
Q1. An element has successive ionisation energies (kJ mol⁻¹): IE₁ = 578, IE₂ = 1817, IE₃ = 2745, IE₄ = 11 577. It most probably belongs to group:
Answer: A. 13
Explanation: The large jump between IE₃ and IE₄ shows three outer electrons have been removed and the fourth comes from an inner shell, so the element has 3 valence electrons (group 13).
Q2. In period 3, which of these elements has a HIGHER first ionisation energy than the element that immediately follows it?
Answer: D. Mg
Explanation: Mg (3s²) has a higher IE₁ than Al (3p¹, a less penetrating electron). Na < Mg, Al < Si and Si < P follow the general rising trend.
Q3. The halogen with the most negative (largest magnitude) electron affinity is:
Answer: B. chlorine
Explanation: Fluorine's very small 2p subshell causes strong electron–electron repulsion, so its electron affinity is slightly smaller in magnitude than that of chlorine.
Q4. Which of the following alkali metal carbonates decomposes to the oxide and CO₂ on ordinary laboratory heating?
Answer: B. Li₂CO₃
Explanation: The small Li⁺ ion polarises the carbonate ion strongly, so Li₂CO₃ decomposes to Li₂O + CO₂; carbonates of Na–Cs are stable at Bunsen temperatures.
Q5. In the Solvay process the overall change is 2NaCl + CaCO₃ → Na₂CO₃ + CaCl₂. If 117 g of NaCl (58.5 g mol⁻¹) gives sodium carbonate (106 g mol⁻¹) with an overall yield of 80%, the mass of Na₂CO₃ obtained is:
Answer: A. 84.8 g
Explanation: NaCl = 2.00 mol, giving 1.00 mol Na₂CO₃ = 106 g theoretical; 80% of 106 = 84.8 g.
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Q6. Which alkaline earth carbonate decomposes at the LOWEST temperature?
Q7. Down group 2 (Mg → Ba), the hydroxides M(OH)₂ show which change?
Q8. Temporary hardness is removed by Clark's process: Ca(HCO₃)₂ + Ca(OH)₂ → 2CaCO₃ + 2H₂O. The mass of Ca(OH)₂ (74 g mol⁻¹) needed to treat 16.2 g of Ca(HCO₃)₂ (162 g mol⁻¹) is:
Q9. The percentage by mass of boron in borax, Na₂B₄O₇·10H₂O (Na = 23, B = 10.8, O = 16, H = 1), is:
Q10. Boric acid, B(OH)₃, is a monobasic acid in water because it:
Q11. 5.4 g of aluminium reacts with excess NaOH solution: 2Al + 2NaOH + 2H₂O → 2NaAlO₂ + 3H₂ (Al = 27; molar volume 22.4 dm³ mol⁻¹). The volume of H₂ evolved at STP is:
Q12. Carbon monoxide can be prepared in the laboratory by dehydrating formic acid. Which reagent is used?
Q13. Hydrolysis of which chlorosilane gives a cross-linked (three-dimensional) silicone polymer?
Q14. The oxidation number of nitrogen in hydrazine, N₂H₄, is:
Q15. Ammonia reacts with excess chlorine as 2NH₃ + 3Cl₂ → N₂ + 6HCl, and the HCl combines with more NH₃. For the overall change 8NH₃ + 3Cl₂ → N₂ + 6NH₄Cl, how many moles of NH₄Cl form per mole of N₂?
Q16. How many P–H bonds are present in a molecule of hypophosphorous acid, H₃PO₂?
Q17. When ozone reacts with moist potassium iodide, O₃ + 2KI + H₂O → I₂ + 2KOH + O₂, how many moles of I₂ are produced per mole of O₃?
Q18. Which allotrope of sulphur is stable at room temperature, and how many atoms does each of its molecules contain?
Q19. A solution of acidified KMnO₄ is decolourised when SO₂ is passed through it. In this reaction SO₂ acts as:
Q20. Chlorine reacts with slaked lime: Ca(OH)₂ + Cl₂ → CaOCl₂ + H₂O (Ca = 40, O = 16, H = 1, Cl = 35.5). The mass of bleaching powder, CaOCl₂, obtained from 3.7 g of Ca(OH)₂ with excess Cl₂ is:
Q21. Which of the following reactions does NOT occur spontaneously in aqueous solution?
Q22. Which sequence correctly lists the hydrogen halides in order of decreasing boiling point?
Q23. Chlorine reacts with hot concentrated NaOH as 3Cl₂ + 6NaOH → 5NaCl + NaClO₃ + 3H₂O. The ratio of moles of NaCl to NaClO₃ formed is:
Q24. Which noble gas has the highest first ionisation energy?
Q25. Sodium hydride reacts with water: NaH + H₂O → NaOH + H₂ (Na = 23, H = 1). The volume of H₂ at STP from 2.4 g of NaH (molar volume 22.4 dm³ mol⁻¹) is:
Q26. Iodine (atomic mass 126.9) follows tellurium (atomic mass 127.6) in the modern periodic table because elements are arranged in order of increasing:
Q27. Which alkali metal nitrate, when strongly heated, gives the metal oxide together with NO₂ and O₂ (like Mg(NO₃)₂)?
Q28. Sodium peroxide reacts with carbon dioxide: 2Na₂O₂ + 2CO₂ → 2Na₂CO₃ + O₂ (Na = 23, O = 16). The mass of oxygen released from 7.8 g of Na₂O₂ is:
Q29. 7.2 g of magnesium (Mg = 24) burns in nitrogen to form Mg₃N₂, which is then fully hydrolysed: Mg₃N₂ + 6H₂O → 3Mg(OH)₂ + 2NH₃ (N = 14, H = 1). The mass of NH₃ obtained is:
Q30. Gypsum, CaSO₄·2H₂O (172 g mol⁻¹), is heated gently to make plaster of Paris, CaSO₄·½H₂O (Ca = 40, S = 32, O = 16, H = 1). The mass of plaster of Paris obtained from 172 g of pure gypsum is: