20. A second order reaction starts with an initial concentration of 0.020M of the reactant. If the rate constant is 10/(M. .), calculate the time required to decrease the initial concentration to 0.005M.
(A)0.069s
(B)10s
(C)15s
(D)0.139s
(E)20s.

16. Which of the following would not be expected to undergo disproportionation?  (A)Cl2(B)(C)(D)(E)

17. Which of the following oxides is amphoteric? (A) Al2O3 (B)B2O3 (C)In2O3 (D)Tl2O3 (E)Tl2O

18. The ionization constants for the diprotic acid H2S are 1.0×10-7 and 1.3×10-13. For 0.1molar solutions of sodium sulfide and sodium hydrogen sulfide, which of the following is true? (A) The solutions are neutral. (B)The sodium sulfide solution is the most basic. (C)Both the solutions are acidic. (D)The sodium hydrogen sulfide solutions is the most basic. (E)Both solutions have the same pH.

19. For the reaction system N2O4(g)≒2NO2(g) at 90°C, Kc = 0.27. For this system, what is Kp? (A) ＞ 0.27 (B)＜ 0.27 (C) = 0.27 (D)We can not determine Kp without additional data. (E)none of these

1.A 300N weight, 5m long rigid uniform ladder is leaning against a smooth vertical wall. A 750N weight man stands on a rung 4m up along the ladder from its base as shown in fig.1. What is the minimum coefficient of the statical friction between the ladder and the floor required to keep the system in equilibrium? The angle is 53.1° on a horizontal beam. (cos53.1° = 0.6, sin53.1° = 0.8) (A)0.22 (B)0.42 (C)0.46 (D)0.54 (E)1.90

2.An imaginary closed surface S of radius R is centered on the origin. A positive charge is originally at the origin, and the flux through hte surface is . The positive charge is slowly moved from the origin to a point R/2 away from the origin. Now the flux is . (A) (B)(C) (D) (E)

3.An incompressible fluid flows through a horizontal pipe. At one point in the pipe the pressure in the fluid is p1 and the fluid speed is v1. Further down the pipe pressure is p2 and the flued speed is 2v1. What can be concluded about p1 and p2? (A) (B) (C) (D) (E)only that

4.A diffraction grating just resolves the wavelengths 400.0 nm and 400.1 nm in the first order. The number of slits in the grating is . (A)400 (B)1000 (C)2500 (D)3000 (E)4000

5.A clear sheet of polaroid is placed on top of a simmilar sheets so that their polarizing axes make an angle of 30° with each other. The ratio of the intensity of emerging light to incident unpolarized light its . (  cos30o,sin30o    ) (A)1/4 (B)1/3 (C)1/2 (D)3/4 (E)3/8

6.What is the intensity ratio of sound for the heavy truck at 1.5m(90dB) to normal conversation at 1m(60dB)? (A)1.5 (B)103 (C)0.67 (D)1030 (E)