23. What is the number of lone pairs of electrons in the NO₂ ^– ion?
(A) 4
(B) 5
(C) 6
(D) 7
(E) 8

19. Which radiation is applied in nuclear magnetic resonance (NMR) technique? (A) X-ray (B) ultraviolet (C) infrared (D) visible (E) radio wave

20. Which of the following reactions is a disproportionation reaction? (A) HCl(aq) + NaOH(aq) → NaCl(aq) + H2O(l) (B) Cl2(aq) + 2I⁻(aq) → I2(aq) + 2Cl⁻(aq) (C) CaSiO3(s) + 8HF(aq) → H2SiF6(aq) + CaF2(aq) + 3H2O(l) (D) AgNO3(aq) + NaCl(aq) → AgCl(aq) + NaNO3(aq) (E) Cl2(aq) + 2NaOH(aq) → NaClO(aq) + NaCl(aq) + H2O(l)

21. Specify the number of unpaired electrons in CoF6 3– (F– ion is a weak field ligand). (A) 0 (B) 1 (C) 2 (D) 4 (E) 5

22. The MnO4ˉ ion is often used to analyze the Fe2+ concentration in an aqueous solution, based on the reaction in acidic condition as follows: (MnO4ˉ + Fe2+ ―→ Fe3+ + Mn2+ ) A 50.00 mL sample of a solution containing Fe2+ requires 40.00 mL of a 0.025 M KMnO4 solution for complete reaction. What is the concentration of the Fe2+ in the original solution? (A) 1.0 × 10-1 M (B) 1.8 × 10-2 M (C) 4.5 × 10-3 M (D) 1.8 × 10-3 M (E) 9.1 × 10-4 M

24. If you add 0.10 M silver nitrate dropwise to a solution consisting of 0.10 M Cl– and 0.10 M CrO4 2–, the precipitates are obtained. Given the Ksp for Ag2CrO4 is 9.0 × 10–12 and that for AgCl is 1.6 × 10–10. Which of the followings will precipitate first? (A) silver chloride (B) silver chromate (C) silver nitrate (D) It cannot be determined by the information given. (E) silver metal

25. When the Pd-106 nucleus is struck with an alpha particle, a proton is produced along with a new element. What is this new element? (A) Cd-112 (B) Cd-109 (C) Ag-108 (D) Ag-109 (E) Ag-110

26. How many unpaired electrons are present in the F2 2+ ion? The order of the molecular orbitals is (σ2s)(σ2s*)(σ2p)(π2p)(π2p*)(σ2p*). (A) 0 (B) 1 (C) 2 (D) 3 (E) 4

27. You are holding four identical balloons each containing 10.0 g of a different gas. The balloon containing which gas is the largest balloon? (A) H2 (B) He (C) Ne (D) O2 (E) All balloons have the same volume.

28. What is the simplest formula of a solid containing three types of atoms in a cubic lattice in which the A, B, and C atoms respectively occupy the corners, the body-center, and the faces-centers of the unit cell? (A) ABC (B) ABC3 (C) ABC6 (D) A8BC6 (E) A4BC3

29. Among the following covalent bonds, which one has the smallest bond energy? (A) C–C (B) C–O (C) C–S (D) C–Cl (E) C–F