49. Which bond is the least polar? (Electronegativities: H = 2.2; N = 3.0; O = 3.5; P = 2.1; S = 2. 5)
(A) N-H
(B) P-H
(C) O-H
(D) S-H
(E) P-S

45. Which of the following process is used by nuclear power plant? (A) Fission (B) Fusion (C) Gamma emission (D) Isotope dilution (E) Radiation

46. What is the complementary sequence (3' → 5') to the DNA segment CAT ? (A) ATG (B) TAA (C) AGG (D) CAT (E) GTA

47. An atom becomes an ion by: (A) gaining or losing protons (B) gaining or losing electrons (C) gaining or losing neutrons (D) gaining or losing mass (E) gaining or losing isotope

48. In order for the electron to return to the ground state, what must happen? (A) energy is absorbed (B) energy is released (C) no energy change (D) electron is lost (E) electron is gained

50. For a double displacement reaction demonstration in class, a solution of potassium iodide and a solution of lead (II) nitrate were combined. A precipitate was formed as a product. What color was the precipitate? (A) white (B) green (C) yellow (D) black (E) red

51. Which one is WRONG for the safety in the laboratory? (A) Wear eye protection at all times. (B) In the event of contact with acids, immediately flood the affected area with copious quantities of water. (C) Never work alone in the laboratory. (D) Never use your mouth to provide suction. (E) It is legal to flush solutions containing heavy metal ions or organic liquids down the drain.

52. Which working electrode is used for pH measurement? (A) Ag/AgCl electrode (B) Calomel electrode (C) Hg electrode (D) Glass electrode (E) Pt electrode

53. Salt A and salt B were dissolved separately in 100 mL beakers of water. The water temperatures were measured and recorded as shown in the table below: Salt A: initial water temp. 25.1°C final water temp. 30.2°C Salt B: initial water temp. 25.1°C final water temp. 20.0°C Which statement is a CORRECT interpretation of these data? (A) The dissolving of only salt A was endothermic. (B) The dissolving of only salt B was exothermic. (C) The dissolving of both salt A and salt B was endothermic. (D) The dissolving of salt A was exothermic and the dissolving of salt B was endothermic. (E) The dissolving of both salt A and salt B was endothermic.

54. How many moles of oxygen gas, O2, will react with 2 moles of nitrogen monoxide gas, NO, according to the following equation? ___ NO (g) + ___ O2(g) ____ NO2(g) [O2 = 32.00 g/mol; NO = 30.01; NO2 = 46.01] (A) 1 mol (B) 2 mol (C) 3 mol (D) 4 mol (E) none of the above

55. Which pair of Lewis electron-dot symbols correctly depicts the elements: boron and carbon? (A) (B) (C) (D) (E)