15. In X-ray spectrum, which of the following statements is correct?
(A) The electron beam is accelerated in the air to strike a target and generate X-rays.
(B) The minimum frequency of X-ray is proportional to the potential difference between anode and cathode.
(C) Most of the generated X-rays are bremsstrahlung radiation.
(D) Characteristic X-rays are the radiation generated by atom nucleus.
(E) Most kinetic energy of electrons is converted to X-rays.

11. A 2.0 kΩ resistor and an initially uncharged 6.0 μF capacitor are connected in series to a 12 V battery. A switch is closed to complete the circuit at t = 0. What is the voltage across the resistor at t = 1.0 s?(A) 0 V (B) 12 V (C) 6 V (D) 3 V (E) 9 V

 12. A 3 μF capacitor is connected in series with a 6 μF capacitor. When a 300 V potential difference is applied across this combination, the total energy stored in the two capacitors is ______. (A) 0.09 J (B) 0.18 J (C) 0.27 J (D) 0.41 J (E) 0.81 J

13. A magnetic field is directed out of the page. Two charged particles enter from the top and take the paths shown in the figure. Which statement is correct? (A) Particle 1 has a positive charge and particle 2 has a negative charge. (B) Particle 1 has a negative charge and particle 2 has a positive charge. (C) Both particles are negatively charged. (D) Both particles are positively charged. (E) The direction of the paths depends on the magnitude of the velocity, not the sign of the charge.

14. In radioactive decays, which of the following statements is incorrect? (A) The energy, momentum, electric charge, and number of nucleons must be conserved. (B) In gamma decay, electromagnetic photons are emitted when a nucleus undergoes a transition from a higher to lower energy. (C) In beta decay, an electron (e- ) or a positron (e+ ) can be emitted by a nucleus. (D) In positron (e+ ) decay, annihilation radiation is generated with different photon energies. (E) The alpha decay is usually observed in the heavy unstable nuclei.

16. Carbon monoxide is commonly used to reduce ores to produce free metals and carbon monoxide is converted to ______. (A) carbon dioxide (B) carbon black (C) methane (D) graphite (E) carbon nanotube

17. Which of the following is the correct order of boiling points for KNO3, CH3OH, C2H6, and Ne? (A) KNO3 < CH3OH < C2H6 < Ne (B) CH3OH < Ne < C2H6 < KNO3 (C) Ne < C2H6 < KNO3 < CH3OH (D) Ne < C2H6 < CH3OH < KNO3 (E) C2H6 < Ne < CH3OH < KNO3

18. How many chiral centers are in this molecule?(A) 0 (B) 1 (C) 2 (D) 3 (E) 4

19. Which of the following statements is incorrect? (A) A triple bond is composed of two π bonds and oneσ bond. (B) σ bonds result from the head-to-head overlap of atomic orbitals. (C) Free rotation does not occur about a double bond. (D) π bonds have electron density on the inter-nuclear axis. (E) More than one of these statements are incorrect.

20. Which of the following statements is incorrect? (A) The reaction constant might change when the reaction temperature changes. (B) The reaction constant won’t change when the concentration of reactants changes. (C) The reaction constant might change when the catalyst is added to the reaction. (D) The activation of energy for a reaction might change when the catalyst is added. (E) The activation of energy for a reaction might change when the reaction temperature changes.

21. When 6 M sodium hydroxide is added to an unknown white solid, the solid is dissolved. What is a possible identity for this solid? (A) Mg(OH)2 (B) Al2(SO4)3 (C) BaCO3 (D) AgBr (E) Ca3(PO4)2