ECAT — Engineering College Admission Test (UET)

ECAT Chemistry — Chemical Bonding (Set 1)

Take the ECAT Chemistry — Chemical Bonding (Set 1): 30 multiple-choice questions (40 minutes) with instant scoring and a full answer review. Covers 30…

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. According to VSEPR theory, the shape of the NH₃ molecule is:
- A. tetrahedral
- B. trigonal planar
- C. T-shaped
- D. trigonal pyramidal ✓
Answer: D. trigonal pyramidal
Explanation: N has 3 bond pairs and 1 lone pair; the four electron pairs are tetrahedral, but the molecular shape is pyramidal.
Q2. The H–O–H bond angle in a water molecule is about:
- A. 109.5°
- B. 104.5° ✓
- C. 120°
- D. 107°
Answer: B. 104.5°
Explanation: Two lone pairs on O repel the bond pairs strongly, squeezing the tetrahedral angle of 109.5° down to about 104.5°.
Q3. The hybridization of carbon in CO₂ is:
- A. sp ✓
- B. sp³
- C. dsp²
- D. sp²
Answer: A. sp
Explanation: C forms two σ bonds and two π bonds with no lone pairs, so it uses two sp hybrid orbitals and the molecule is linear.
Q4. The hybridization of sulphur in SF₆ is:
- A. sp³d² ✓
- B. dsp²
- C. sp³
- D. sp³d
Answer: A. sp³d²
Explanation: S forms six σ bonds with no lone pairs, so it needs six hybrid orbitals (sp³d²), giving an octahedral shape.
Q5. The geometry of the PCl₅ molecule is:
- A. square pyramidal
- B. tetrahedral
- C. octahedral
- D. trigonal bipyramidal ✓
Answer: D. trigonal bipyramidal
Explanation: P has five bond pairs and no lone pairs (sp³d), which take up a trigonal bipyramidal arrangement.

The other 25 questions

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Q6. Which molecule has zero dipole moment?
- A. CHCl₃
- B. BF₃
- C. NH₃
- D. H₂O
Q7. How many σ and π bonds are present in an ethyne (C₂H₂) molecule?
- A. 3 σ and 2 π
- B. 2 σ and 3 π
- C. 3 σ and 1 π
- D. 5 σ and 0 π
Q8. According to molecular orbital theory, the bond order of the superoxide ion O₂⁻ is:
- A. 2.5
- B. 1
- C. 1.5
- D. 2
Q9. Which of these molecules is paramagnetic?
- A. H₂
- B. N₂
- C. O₂
- D. F₂
Q10. Which species has the highest bond order?
- A. F₂
- B. O₂
- C. N₂
- D. N₂⁺
Q11. Which bond is the most polar?
- A. H–F
- B. H–Cl
- C. H–I
- D. H–Br
Q12. The first ionization energy of Al is lower than that of Mg because:
- A. the electron removed from Al is in a 3p orbital, which is higher in energy and more shielded
- B. Al has a larger number of shells
- C. the electron removed from Mg is in a 3p orbital
- D. Al has a smaller nuclear charge
Q13. Which element has the most negative (highest) electron affinity?
- A. F
- B. Br
- C. O
- D. Cl
Q14. HCl has a dipole moment of 1.03 D and a bond length of 1.27 Å. If the bond were 100% ionic its dipole moment would be 4.8 × 1.27 D. The percentage ionic character of HCl is about:
- A. 17%
- B. 21%
- C. 8%
- D. 83%
Q15. A coordinate covalent (dative) bond is present in:
- A. NH₃
- B. CH₄
- C. NH₄⁺
- D. H₂O
Q16. Which carbon–carbon bond has the shortest bond length?
- A. C≡C in ethyne
- B. C=C in ethene
- C. C–C in ethane
- D. C–C in benzene
Q17. In the NH₄⁺ ion, the hybridization of nitrogen and the H–N–H bond angle are:
- A. dsp² and 90°
- B. sp³ and 107°
- C. sp² and 120°
- D. sp³ and 109.5°
Q18. The shape of the SO₂ molecule is:
- A. bent (angular)
- B. linear
- C. tetrahedral
- D. trigonal planar
Q19. The bond angles decrease in the order CH₄ > NH₃ > H₂O mainly because:
- A. the number of bonds increases
- B. electronegativity of the central atom decreases
- C. lone pair–bond pair repulsion is greater than bond pair–bond pair repulsion
- D. the central atom becomes larger
Q20. The Cl–Cl bond length in Cl₂ is 198 pm. The covalent radius of chlorine is:
- A. 396 pm
- B. 99 pm
- C. 49.5 pm
- D. 198 pm
Q21. ClF₃ has 3 bond pairs and 2 lone pairs on chlorine. Its molecular shape is:
- A. trigonal planar
- B. trigonal pyramidal
- C. see-saw
- D. T-shaped
Q22. Which statement about a π bond is correct?
- A. It is formed by head-on overlap of orbitals
- B. It allows free rotation about the bond axis
- C. It can be formed without a σ bond already present
- D. It is weaker than a σ bond between the same atoms because the overlap is less effective
Q23. Which chloride has the most covalent character?
- A. LiCl
- B. NaCl
- C. KCl
- D. CsCl
Q24. Ice is less dense than liquid water because:
- A. ice contains dissolved air
- B. ice molecules have no hydrogen bonds
- C. covalent bonds in ice are longer
- D. hydrogen bonding in ice gives an open cage-like structure with empty spaces
Q25. Use the data (kJ mol⁻¹) to find the standard enthalpy of formation of NaCl: sublimation of Na +108, ionization of Na +496, ½ dissociation of Cl₂ +121, electron affinity of Cl −349, lattice energy −787.
- A. −411 kJ mol⁻¹
- B. −1861 kJ mol⁻¹
- C. +411 kJ mol⁻¹
- D. −289 kJ mol⁻¹
Q26. Bond energies (kJ mol⁻¹): H–H 436, Cl–Cl 243, H–Cl 432. The enthalpy change for H₂ + Cl₂ → 2HCl is:
- A. +185 kJ
- B. −432 kJ
- C. −185 kJ
- D. −247 kJ
Q27. According to MO theory, the He₂ molecule does not exist because:
- A. its bond order is 2
- B. helium has no valence electrons
- C. its bond order is zero
- D. helium atoms are too large
Q28. Although each C=O bond is polar, CO₂ has zero dipole moment because:
- A. CO₂ is an ionic compound
- B. the molecule is linear and the two bond dipoles cancel
- C. the molecule is bent
- D. carbon and oxygen have equal electronegativity
Q29. In ethene (C₂H₄), each carbon atom is:
- A. sp hybridized with bond angles of 180°
- B. sp² hybridized with bond angles of about 120°
- C. sp³ hybridized with bond angles of 109.5°
- D. sp² hybridized with bond angles of 90°
Q30. Which species is isoelectronic with CH₄ and has the same tetrahedral shape?
- A. BH₃
- B. H₃O⁺
- C. NH₄⁺
- D. NH₃