ECAT — Engineering College Admission Test (UET)
Take the ECAT Chemistry — Periodic Table, s- and p-Block Elements (Set 2): 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. Down a group of the periodic table, the first ionization energy generally decreases mainly because:
Answer: A. The outer electron is farther from the nucleus and more shielded by inner shells
Explanation: Each new shell places the valence electron farther out; increased shielding outweighs the rising nuclear charge.
Q2. The first ionization energy of beryllium (899 kJ mol⁻¹) is higher than that of boron (801 kJ mol⁻¹) because:
Answer: A. The 2p electron of boron is higher in energy and shielded by the 2s² pair
Explanation: B loses a 2p electron, which is less penetrating and partly shielded by the filled 2s subshell; Be must lose an electron from a stable 2s² pair.
Q3. Beryllium shows a diagonal relationship with aluminium. One property they share is that:
Answer: C. Their oxides and hydroxides are amphoteric
Explanation: BeO/Be(OH)₂ and Al₂O₃/Al(OH)₃ dissolve in both acids and alkalis, reflecting similar charge-to-size ratios of Be²⁺ and Al³⁺.
Q4. Among the alkali metal ions, which has the highest hydration energy?
Answer: B. Li⁺
Explanation: Li⁺ is the smallest ion with the highest charge density, so it attracts water molecules most strongly.
Q5. When potassium burns in an excess of oxygen, the main product is:
Answer: C. KO₂
Explanation: Li gives the normal oxide, Na mainly the peroxide, and the larger K, Rb and Cs form superoxides (MO₂), stabilized by the large cation.
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Q6. Sodium dissolves in liquid ammonia to give a deep blue solution. The colour is due to:
Q7. On strong heating, sodium nitrate decomposes to give:
Q8. When magnesium ribbon burns in air, the products are:
Q9. Temporary hardness of water, which can be removed by boiling, is caused by dissolved:
Q10. Lime water turns milky when CO₂ is bubbled through it, but becomes clear again with excess CO₂. The clear solution contains:
Q11. On strong heating, borax swells up and finally fuses into a transparent glassy bead consisting of:
Q12. Aluminium dissolves in hot aqueous NaOH. The products are:
Q13. In the vapour state at moderate temperatures, aluminium chloride exists as Al₂Cl₆ because:
Q14. SiCl₄ is readily hydrolysed by water but CCl₄ is not. This is because:
Q15. Nitrogen gas is very unreactive at room temperature mainly because:
Q16. Copper reacts with concentrated nitric acid to give a brown gas. The gas is:
Q17. Aqua regia, which dissolves gold and platinum, is a mixture of:
Q18. Red phosphorus is much less reactive than white phosphorus because:
Q19. Phosphorous acid, H₃PO₃, is dibasic (not tribasic) because:
Q20. In the contact process, SO₃ is absorbed in concentrated H₂SO₄ to form oleum rather than directly in water because:
Q21. Concentrated H₂SO₄ turns sugar into a black mass of carbon. Here the acid acts as:
Q22. Hydrofluoric acid is a weak acid in water whereas hydrochloric acid is strong. The main reason is that:
Q23. Fluorine shows only the −1 oxidation state in its compounds, unlike chlorine, because fluorine:
Q24. Using VSEPR theory, the shape of the XeF₄ molecule is:
Q25. Which oxide of period 3 is the most strongly acidic?
Q26. What mass of sodium reacts with excess water to liberate 2.24 dm³ of H₂ at STP (Na = 23)?
Q27. What mass of quicklime is obtained by completely heating 25 g of limestone, CaCO₃ (Ca = 40)?
Q28. The blue colour formed when iodine is added to starch solution is used to detect:
Q29. Hydrogen is sometimes placed with the halogens in group 17 because, like them, it:
Q30. When gypsum is heated above about 200°C it loses all its water of crystallization. The product, which no longer sets with water, is called: