ECAT — Engineering College Admission Test (UET)

ECAT Chemistry — Periodic Table, s- and p-Block Elements (Set 1)

Take the ECAT Chemistry — Periodic Table, s- and p-Block Elements (Set 1): 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. The modern periodic law states that the properties of elements are periodic functions of their:
- A. atomic numbers ✓
- B. densities
- C. atomic masses
- D. numbers of neutrons
Answer: A. atomic numbers
Explanation: Moseley showed that atomic number, not atomic mass, is the true basis for arranging elements.
Q2. An element with atomic number 17 is placed in:
- A. period 3, group 7 (VIIB)
- B. period 4, group 17
- C. period 3, group 17 (VIIA) ✓
- D. period 2, group 17
Answer: C. period 3, group 17 (VIIA)
Explanation: Configuration 2, 8, 7: three shells give period 3 and seven valence electrons in s and p give group 17 (halogens).
Q3. Which atom has the largest atomic radius?
- A. Cl
- B. Mg
- C. Al
- D. Na ✓
Answer: D. Na
Explanation: Across period 3 the nuclear charge increases while the shell stays the same, so radius decreases from Na to Cl.
Q4. The first ionization energy of nitrogen is higher than that of oxygen because:
- A. nitrogen has a larger nuclear charge
- B. oxygen has a smaller atomic radius
- C. nitrogen has a stable half-filled 2p subshell ✓
- D. oxygen has a half-filled 2p subshell
Answer: C. nitrogen has a stable half-filled 2p subshell
Explanation: N (2p³) has a half-filled subshell; in O (2p⁴) one electron is paired and electron repulsion makes it easier to remove.
Q5. Although Cs loses its valence electron more easily in the gas phase, lithium has the most negative standard electrode potential among alkali metals. This is mainly due to:
- A. the low melting point of lithium
- B. the low ionization energy of lithium
- C. the very high hydration energy of the small Li⁺ ion ✓
- D. the large atomic radius of lithium
Answer: C. the very high hydration energy of the small Li⁺ ion
Explanation: The tiny Li⁺ ion is strongly hydrated, releasing enough energy to make Li → Li⁺(aq) the most favourable.

The other 25 questions

Take the timed test (free, no sign-up) to see your score and the answer and explanation for every question.

Q6. Which period 3 oxide is amphoteric?
- A. Al₂O₃
- B. MgO
- C. Na₂O
- D. SO₃
Q7. Which hydride reacts with water to release hydrogen gas?
- A. NH₃
- B. NaH
- C. HCl
- D. CH₄
Q8. Lithium resembles magnesium in many properties (e.g. both form nitrides directly). This is called:
- A. isomorphism
- B. inert pair effect
- C. diagonal relationship
- D. lanthanide contraction
Q9. Potassium salts give which colour in a flame test?
- A. golden yellow
- B. crimson red
- C. brick red
- D. lilac (violet)
Q10. In Down's cell, CaCl₂ is added to the fused NaCl in order to:
- A. increase the yield of chlorine
- B. lower the melting point of the electrolyte
- C. act as a catalyst at the cathode
- D. prevent the formation of sodium
Q11. The main products of Nelson's cell (electrolysis of brine) are:
- A. Na₂CO₃ and Cl₂
- B. Na, Cl₂ and O₂
- C. NaOH, H₂ and Cl₂
- D. NaClO₃ and H₂
Q12. Which alkaline earth metal sulphate is the least soluble in water?
- A. BaSO₄
- B. BeSO₄
- C. MgSO₄
- D. CaSO₄
Q13. Which hydroxide is the strongest base?
- A. Ba(OH)₂
- B. Mg(OH)₂
- C. Ca(OH)₂
- D. Be(OH)₂
Q14. Which carbonate decomposes most easily on heating?
- A. BeCO₃
- B. BaCO₃
- C. CaCO₃
- D. MgCO₃
Q15. Plaster of Paris is obtained by heating gypsum to about 120°C. Its formula is:
- A. CaSO₄·2H₂O
- B. (CaSO₄)₂·H₂O
- C. CaSO₄
- D. CaSO₄·5H₂O
Q16. Slaked lime is:
- A. CaCl₂
- B. CaO
- C. CaCO₃
- D. Ca(OH)₂
Q17. Boric acid, H₃BO₃, behaves in water as a:
- A. strong base
- B. weak monobasic Lewis acid
- C. weak tribasic Brønsted acid
- D. strong tribasic protic acid
Q18. Aluminium does not dissolve in concentrated HNO₃ because:
- A. HNO₃ is a reducing agent
- B. aluminium is below hydrogen in the electrochemical series
- C. aluminium forms a soluble nitrate
- D. a thin protective oxide layer makes it passive
Q19. In group 14, the +2 oxidation state of lead is more stable than +4. This is due to:
- A. the high electronegativity of lead
- B. the inert pair effect
- C. the shielding by p electrons
- D. the diagonal relationship
Q20. CO₂ is a gas at room temperature whereas SiO₂ is a hard, high-melting solid because:
- A. SiO₂ is an ionic compound
- B. SiO₂ forms a giant covalent network in which each Si is bonded to four O atoms
- C. CO₂ molecules are held by hydrogen bonds
- D. silicon forms stronger π bonds than carbon
Q21. In Ostwald's process for the manufacture of nitric acid, ammonia is first oxidized using:
- A. nickel catalyst
- B. an iron catalyst
- C. V₂O₅ catalyst
- D. a platinum (Pt–Rh) gauze catalyst
Q22. The oxidation number of nitrogen in nitrous oxide, N₂O, is:
- A. −1
- B. +4
- C. +2
- D. +1
Q23. PCl₅ reacts completely with excess water to give:
- A. P₂O₅ and Cl₂
- B. H₃PO₃ and HCl
- C. PH₃ and HOCl
- D. H₃PO₄ and HCl
Q24. In the contact process for sulphuric acid, the catalyst used to convert SO₂ into SO₃ is:
- A. Pt–Rh
- B. V₂O₅
- C. Fe
- D. Ni
Q25. The bond dissociation energy of F₂ is lower than that of Cl₂ because:
- A. fluorine is less electronegative than chlorine
- B. the F–F bond is longer than the Cl–Cl bond
- C. the lone pairs on the two small F atoms repel each other strongly
- D. fluorine has d orbitals available
Q26. Which hydrogen halide has the highest boiling point?
- A. HF
- B. HI
- C. HBr
- D. HCl
Q27. Which halogen can liberate bromine from aqueous KBr?
- A. Br₂
- B. Cl₂
- C. At₂
- D. I₂
Q28. The first true noble gas compound, prepared by Neil Bartlett in 1962, was:
- A. KrF₂
- B. XePtF₆
- C. XeO₃
- D. XeF₄
Q29. Bleaching powder is commonly represented as:
- A. Ca(ClO₃)₂
- B. NaOCl
- C. Ca(OCl)Cl
- D. CaCl₂
Q30. Which oxyacid of chlorine is the strongest acid?
- A. HClO₂
- B. HClO₄
- C. HClO₃
- D. HClO