28. Which of the following can be identified as a set of isotopes?
Atomic nuclei contain
I. 20 protons and 20 neutrons. II. 20 protons and 22 neutrons.
III. 21 protons and 19 neutrons. fV. 20 neutrons and 18 protons.
V. 21 protons and 20 neutrons.
(A) I, IV and II, V
(B) I, II and III, fV
(C) I, III and II, V
(D) II, IV and III, V
(E) I, II and III, V

24. Arrange the following bonds in order of decreasing polarity:1. H-H 2. C-F 3. Al-F 4. N-O(A) 1＞2＞3＞4 (B) 3＞2＞4＞1 (C) 1＞3＞2＞4(D) 1＞4＞2＞3 (E) 3＞4＞2＞1

25. The density of a gas is 2 g/L at 3 atm and 27oC. What is the molar mass of the gas (g/mol)?(A) 1.48 (B) 32 (C) 149.6 (D) 9.3 (E) 16.4

26. Which of the following reactions does not involve oxidation-reduction?(A) CH4 + 3O2→ 2H2O + CO2 (B) PCl3 + Cl2 →PCl5(C) 2Na + 2H2O →2NaOH + H2 (D) MnO2 + 4HCl→ Cl2 + 2H2O + MnCl2(E) CO2 + 2LiOH →Li2CO3 + H2O

27. Calculate the standard change in enthalpy for the reaction and select the correct answer: (A) exothermic reaction(B) endothermic reaction(C) no energy change for this reaction(D) Lack of makes calculation impossible.(E) None of the above.

29. Which of the following represents the electron configuration for an excited state of an oxygenatom?(A) 1s22s 22p4 (B) 1s 22s 22p5 (C) 1s22s22p33s1(D) 1s 22s 22p6 (E) 1s22s22p3

30. The nucleus decays to form by producing α and β particles. What is the number of β particles produced?(A) 1 (B) 2 (C) 4 (D) 6 (E) 8

31. A 0.25 kg block oscillates on the end of the spring with a spring constant of 133.3 N/m. If the system has an energy of 6.0 J, then the amplitude of the oscillation is _____.(A) 0.09 m (B) 0.15 m (C) 0.30 m (D) 0.54 m (E) 0.60 m

32. fn designing buildings to be erected in an area prone to earthquakes, what relationship should the designer try to achieve between the natural frequency of the building and the typical earthquake frequencies?(A) The natural frequency of the building should be exactly the same as typical earthquakefrequencies.(B) The natural frequency of the building should be very different from typical earthquakefrequencies.(C) The natural frequency of the building should be almost the same as typical earthquakefrequencies but slightly higher.(D) The natural frequency of the building should be almost the same as typical earthquakefrequencies but slightly lower.(E) No need to consider.

33. A 2 kg object is attached to an ideal massless horizontal spring of spring constant 100.0 N/m andis at rest on a frictionless horizontal table. The spring is aligned along the x-axis and is fixed to apeg in the table. Suddenly this mass is struck by another 2 kg object traveling along the x-axis at 3 m/s, and the two masses stick together. What are the amplitude and period of the oscillationsthat result from this collision?(A) 0.30 m, 1.26 s (B) 0.30 m, 0.88 s (C) 0.42 m, 0.88 s(D) 0.42 m, 1.26 s (E) 0.42 m, 5.00 s

34. Two blocks connected by a cord (of negligible mass) that passes over a frictionlesspulley (also of negligible mass). The arrangement is known as Atwood’s machine.One block has mass m1=1.3 kg; the other has mass m2=2.8 kg. What is the magnitudeof the tension of the cord?(A) 11.0 N (B) 12.8 N (C) 15.7 N (D) 17.7 N (E) 20.0 N