ap chemistry 2차 - unit 1

1. Which element reacts violently with water at 298 K?

(A) Magnesium (Mg)
(B) Aluminum (Al)
(C) Potassium (K)
(D) Silicon (Si)

View Answer

Correct Answer: (C) Potassium (K)
Explanation: Group 1 alkali metals like potassium react violently with water to produce hydrogen gas and hydroxides.

2. Which element has the highest first ionization energy?

(A) Sodium (Na)
(B) Magnesium (Mg)
(C) Neon (Ne)
(D) Argon (Ar)

View Answer

Correct Answer: (C) Neon (Ne)
Explanation: Noble gases have the highest ionization energies in their periods due to stable electron configurations.

3. Which has the highest electron affinity?

(A) Oxygen (O)
(B) Fluorine (F)
(C) Sulfur (S)
(D) Chlorine (Cl)

View Answer

Correct Answer: (D) Chlorine (Cl)
Explanation: Chlorine has higher electron affinity than fluorine due to reduced electron-electron repulsion.

4. Which has the highest electronegativity?

(A) Carbon (C)
(B) Nitrogen (N)
(C) Oxygen (O)
(D) Fluorine (F)

View Answer

Correct Answer: (D) Fluorine (F)
Explanation: Fluorine is the most electronegative element (Pauling scale = 4.0).

5. Which has the largest atomic radius?

(A) Lithium (Li)
(B) Sodium (Na)
(C) Potassium (K)
(D) Rubidium (Rb)

View Answer

Correct Answer: (D) Rubidium (Rb)
Explanation: Atomic radius increases down a group due to additional electron shells.

6. Which has the most metallic character?

(A) Beryllium (Be)
(B) Calcium (Ca)
(C) Strontium (Sr)
(D) Barium (Ba)

View Answer

Correct Answer: (D) Barium (Ba)
Explanation: Metallic character increases down Group 2.

7. In a PES graph for oxygen, the peak at highest binding energy corresponds to:

(A) 2p electron
(B) 2s electron
(C) 1s electron
(D) 3s electron

View Answer

Correct Answer: (C) 1s electron
Explanation: In PES, electrons in lower orbitals (e.g., 1s) have higher binding energy due to being closer to the nucleus.

8. Strontium has isotopes: ⁸⁶Sr (85.91 amu), ⁸⁷Sr (86.91 amu), ⁸⁸Sr (87.91 amu). Average mass is 87.62 amu. Which must be true?

(A) ⁸⁶Sr is most abundant
(B) ⁸⁷Sr is most abundant
(C) ⁸⁸Sr is most abundant
(D) ⁸⁶Sr is least abundant

View Answer

Correct Answer: (C) ⁸⁸Sr is most abundant
Explanation: Average mass (87.62) is closest to ⁸⁸Sr mass (87.91), indicating highest abundance.

9. Which property decreases left to right across a period (K to Br)?

(A) Electronegativity
(B) Electron affinity
(C) Atomic radius
(D) Oxidation number

View Answer

Correct Answer: (C) Atomic radius
Explanation: Atomic radius decreases due to increasing effective nuclear charge.

10. False statement about alkali metals:

(A) Reactivity increases down the group
(B) They form strong acids with water
(C) They have low ionization energies
(D) They are silver solids at 298K

View Answer

Correct Answer: (B) They form strong acids with water
Explanation: Alkali metals form basic solutions (e.g., NaOH), not acids.

11. Which has chemical properties most similar to phosphorus?

(A) Sulfur (S)
(B) Selenium (Se)
(C) Oxygen (O)
(D) Arsenic (As)

View Answer

Correct Answer: (D) Arsenic (As)
Explanation: Both in Group 15 with similar valence electron configuration.

12. Which pair is isoelectronic?

(A) Kr and Br⁺
(B) F⁻ and Na⁺
(C) Sc and Ti⁻
(D) Be²⁺ and Ne

View Answer

Correct Answer: (D) Be²⁺ and Ne
Explanation: Both have 10 electrons (Be²⁺: 4-2=2e⁻, Ne: 10e⁻).

13. Which ion has the same electrons as I⁻?

(A) Sr²⁺
(B) Rb⁺
(C) Cs⁺
(D) Br⁻

View Answer

Correct Answer: (D) Br⁻
Explanation: Both I⁻ (53+1=54e⁻) and Br⁻ (35+1=36e⁻) have 54 electrons? Correction: Br⁻ has 36e⁻, I⁻ has 54e⁻. 
Correct pair: Xe (54e⁻) is isoelectronic with I⁻.

14. Why is F⁻ smaller than O²⁻?

(A) F⁻ has more massive nucleus
(B) F⁻ has higher electronegativity
(C) F⁻ has greater nuclear charge
(D) F⁻ has more electrons

View Answer

Correct Answer: (C) F⁻ has greater nuclear charge
Explanation: Fluorine (Z=9) vs Oxygen (Z=8) - higher Z pulls electrons closer.

15. False statement about periodic table:

(A) Alkali metal reactivity increases down group
(B) Halogen reactivity decreases down group
(C) Group 1/2 metals form basic solutions with water
(D) Noble gases only exist as monatomic gases

View Answer

Correct Answer: (D) Noble gases only exist as monatomic gases
Explanation: Some noble gases form compounds (e.g., XeF₄).

16. Diatomic elemental gases at STP include:

(A) H, N, O
(B) H, N, O, F, Cl
(C) H, N, O, Cl, Br, I
(D) H, N, O, Cl, He, Ne

View Answer

Correct Answer: (B) H, N, O, F, Cl
Explanation: F and Cl are gases at STP; Br and I are liquids/solids.

17. As atomic number increases from 11 to 17:

(A) Atomic radius remains constant
(B) Atomic radius increases
(C) Atomic radius decreases
(D) Atomic radius increases then decreases

View Answer

Correct Answer: (C) Atomic radius decreases
Explanation: From Na (Z=11) to Cl (Z=17), radius decreases across period.

18. Effective nuclear charge difference between K and Kr:

(A) Kr has higher first ionization energy
(B) Kr has higher proton-to-electron ratio
(C) K valence electrons experience less shielding
(D) Kr valence electrons experience less shielding

View Answer

Correct Answer: (A) Kr has higher first ionization energy
Explanation: Kr (noble gas) has full valence shell → higher IE than K (alkali metal).

19. Based on ionization energies, which element is X?

Ionization Energies (kJ/mol):
1st: 899, 2nd: 1757, 3rd: 14849

(A) Li
(B) Be
(C) Al
(D) Si

View Answer

Correct Answer: (C) Al
Explanation: Large jump after 3rd IE indicates Group 13 element (valence electrons removed).

20. Large ionization energy drops between elements 2-3, 10-11, 18-19 occur because elements 2,10,18 have:

(A) Smaller atomic radii
(B) Greater electron affinity
(C) Greater effective nuclear charge
(D) Both A and C

View Answer

Correct Answer: (D) Both A and C
Explanation: Noble gases (2,10,18) have small radii and high Z_eff → high IE.

21. Which electron configuration represents an excited state?

(A) 1s²2s²2p⁶
(B) 1s²2s²2p⁵3s²
(C) 1s²2s²2p⁶3s¹
(D) 1s²2s²2p⁶3s²3p⁵

View Answer

Correct Answer: (B) 1s²2s²2p⁵3s²
Explanation: An electron has jumped from 2p to 3s orbital (ground state should be 1s²2s²2p⁶).

22. Which pair has the same number of valence electrons?

(A) Na and Mg
(B) Al and Si
(C) P and S
(D) Cl and Ar

View Answer

Correct Answer: (D) Cl and Ar
Explanation: Both have 7 valence electrons? Correction: Cl (Group 17) has 7, Ar (Group 18) has 8. 
Correct pair: N and P (both Group 15).

23. As you move down Group 17, what happens to atomic radius?

(A) Decreases
(B) Increases
(C) Remains constant
(D) Increases then decreases

View Answer

Correct Answer: (B) Increases
Explanation: Each period adds a new electron shell, increasing atomic radius.

24. Which element has the highest second ionization energy?

(A) Lithium (Li)
(B) Beryllium (Be)
(C) Sodium (Na)
(D) Magnesium (Mg)

View Answer

Correct Answer: (A) Lithium (Li)
Explanation: Removing a second electron from Li⁺ (helium configuration) requires exceptionally high energy.

25. Which ion has the largest radius?

(A) O^2-
(B) F^-
(C) Na⁺
(D) Mg²⁺

View Answer

Correct Answer: (A) O^2-
Explanation: Highest electron-to-proton ratio results in largest ionic radius.

26. Why does nitrogen have higher first ionization energy than oxygen?

(A) Smaller atomic radius
(B) Half-filled p-subshell stability
(C) Higher nuclear charge
(D) Greater electron affinity

View Answer

Correct Answer: (B) Half-filled p-subshell stability
Explanation: Nitrogen's 2p³ configuration is more stable than oxygen's 2p⁴.

27. Which element forms colored compounds?

(A) Sodium (Na)
(B) Calcium (Ca)
(C) Chromium (Cr)
(D) Aluminum (Al)

View Answer

Correct Answer: (C) Chromium (Cr)
Explanation: Transition metals like chromium form colored compounds due to d-d electron transitions.

28. Which element has the largest atomic radius in Period 4?

(A) Potassium (K)
(B) Gallium (Ga)
(C) Selenium (Se)
(D) Krypton (Kr)

View Answer

Correct Answer: (A) Potassium (K)
Explanation: Atomic radius decreases across a period. K (Group 1) has the largest radius in Period 4.

29. Which element has the highest melting point?

(A) Carbon (C)
(B) Tungsten (W)
(C) Iron (Fe)
(D) Copper (Cu)

View Answer

Correct Answer: (B) Tungsten (W)
Explanation: Tungsten has the highest melting point of all metals (3422°C).

30. Which element is a metalloid?

(A) Germanium (Ge)
(B) Gallium (Ga)
(C) Selenium (Se)
(D) Bromine (Br)

View Answer

Correct Answer: (A) Germanium (Ge)
Explanation: Metalloids exhibit properties of both metals and nonmetals (along the staircase line).

31. Which ion is isoelectronic with Argon?

(A) K⁺
(B) Cl^-
(C) S^2-
(D) All of the above

View Answer

Correct Answer: (D) All of the above
Explanation: All have 18 electrons (same as Ar).

32. Which element has the highest electron affinity?

(A) Fluorine (F)
(B) Chlorine (Cl)
(C) Oxygen (O)
(D) Sulfur (S)

View Answer

Correct Answer: (B) Chlorine (Cl)
Explanation: Larger atomic size reduces electron-electron repulsion compared to fluorine.

33. Which element is a liquid at room temperature?

(A) Bromine (Br)
(B) Chlorine (Cl)
(C) Iodine (I)
(D) Astatine (At)

View Answer

Correct Answer: (A) Bromine (Br)
Explanation: Only nonmetal liquid at 25°C (mercury is metal liquid).

34. Which element has the most unpaired electrons?

(A) Nitrogen (N)
(B) Oxygen (O)
(C) Phosphorus (P)
(D) Chromium (Cr)

View Answer

Correct Answer: (D) Chromium (Cr)
Explanation: Cr has 6 unpaired electrons ([Ar] 4s¹3d⁵ configuration).

35. Which element has the highest first ionization energy in Group 2?

(A) Beryllium (Be)
(B) Magnesium (Mg)
(C) Calcium (Ca)
(D) Barium (Ba)

View Answer

Correct Answer: (A) Beryllium (Be)
Explanation: Ionization energy decreases down a group. Be (top of Group 2) has the highest IE.

36. Which element has the highest electronegativity?

(A) Sodium (Na)
(B) Magnesium (Mg)
(C) Aluminum (Al)
(D) Silicon (Si)

View Answer

Correct Answer: (D) Silicon (Si)
Explanation: Electronegativity increases across a period (left to right).

37. Which element forms an alkaline solution with water?

(A) Carbon (C)
(B) Sulfur (S)
(C) Calcium (Ca)
(D) Chlorine (Cl)

View Answer

Correct Answer: (C) Calcium (Ca)
Explanation: Group 2 metals form hydroxides (alkaline solutions) with water.

38. Which element is a noble gas?

(A) Fluorine (F)
(B) Neon (Ne)
(C) Sodium (Na)
(D) Magnesium (Mg)

View Answer

Correct Answer: (B) Neon (Ne)
Explanation: Noble gases are Group 18 elements with full valence shells.

39. Which element has the smallest atomic radius?

(A) Lithium (Li)
(B) Beryllium (Be)
(C) Boron (B)
(D) Carbon (C)

View Answer

Correct Answer: (D) Carbon (C)
Explanation: Atomic radius decreases across a period (left to right).

40. Which element has the highest first ionization energy?

(A) Potassium (K)
(B) Calcium (Ca)
(C) Gallium (Ga)
(D) Krypton (Kr)

View Answer

Correct Answer: (D) Krypton (Kr)
Explanation: Noble gases have the highest ionization energies in their periods.

41. Which halogen has the lowest electron affinity?

(A) Fluorine (F)
(B) Chlorine (Cl)
(C) Bromine (Br)
(D) Iodine (I)

View Answer

Correct Answer: (D) Iodine (I)
Explanation: Electron affinity decreases down Group 17 due to increasing atomic size.

42. Which element is an alkali metal?

(A) Beryllium (Be)
(B) Magnesium (Mg)
(C) Potassium (K)
(D) Calcium (Ca)

View Answer

Correct Answer: (C) Potassium (K)
Explanation: Alkali metals are Group 1 elements (excluding hydrogen).

43. Which element has the highest density?

(A) Lithium (Li)
(B) Sodium (Na)
(C) Potassium (K)
(D) Osmium (Os)

View Answer

Correct Answer: (D) Osmium (Os)
Explanation: Transition metals like osmium have the highest densities (22.59 g/cm³).

44. Which element is the best conductor of electricity?

(A) Silicon (Si)
(B) Sulfur (S)
(C) Copper (Cu)
(D) Iodine (I)

View Answer

Correct Answer: (C) Copper (Cu)
Explanation: Metals like copper have free electrons that conduct electricity efficiently.

45. Which element has the most metallic character in Period 3?

(A) Sodium (Na)
(B) Magnesium (Mg)
(C) Aluminum (Al)
(D) Silicon (Si)

View Answer

Correct Answer: (A) Sodium (Na)
Explanation: Metallic character decreases across a period. Na (Group 1) is the most metallic.

46. Which element is paramagnetic?

(A) Helium (He)
(B) Beryllium (Be)
(C) Oxygen (O)
(D) Neon (Ne)

View Answer

Correct Answer: (C) Oxygen (O)
Explanation: Paramagnetic substances have unpaired electrons (oxygen has two unpaired electrons).

47. Which element has the lowest electronegativity?

(A) Cesium (Cs)
(B) Francium (Fr)
(C) Barium (Ba)
(D) Radium (Ra)

View Answer

Correct Answer: (B) Francium (Fr)
Explanation: Electronegativity decreases down a group; Fr has the lowest value (0.7).

48. Which element is a semiconductor?

(A) Sodium (Na)
(B) Aluminum (Al)
(C) Silicon (Si)
(D) Silver (Ag)

View Answer

Correct Answer: (C) Silicon (Si)
Explanation: Semiconductors like silicon have electrical conductivity between conductors and insulators.

49. Which pair shows the correct trend in electronegativity?

(A) K > Rb
(B) O > F
(C) C > N
(D) Cl > S

View Answer

Correct Answer: (D) Cl > S
Explanation: Electronegativity increases across a period (S < Cl) and decreases down a group.

50. Which element is the most reactive nonmetal?

(A) Fluorine (F)
(B) Chlorine (Cl)
(C) Oxygen (O)
(D) Sulfur (S)

View Answer

Correct Answer: (A) Fluorine (F)
Explanation: Fluorine is the most electronegative and reactive nonmetal.

51. Which photon has the greatest energy?

(A) λ = 700 nm
(B) λ = 550 nm
(C) λ = 400 nm
(D) λ = 1200 nm

View Answer

Correct Answer: (C) λ = 400 nm
Explanation: E = hc/λ → shorter wavelength means higher energy.

52. Which pair of ions experiences the strongest Coulombic attraction?

(A) Na⁺ and Cl⁻
(B) Mg²⁺ and O²⁻
(C) K⁺ and Br⁻
(D) Ca²⁺ and F⁻

View Answer

Correct Answer: (B) Mg²⁺ and O²⁻
Explanation: Coulombic force ∝ q₁q₂/r² → higher charges result in stronger attraction.

53. What is the correct ground-state configuration of chromium (Cr)?

(A) [Ar] 4s² 3d⁴
(B) [Ar] 4s¹ 3d⁵
(C) [Ar] 4s² 3d³ 4p¹
(D) [Ar] 4s⁰ 3d⁶

View Answer

Correct Answer: (B) [Ar] 4s¹ 3d⁵
Explanation: Cr and Cu are exceptions due to d-subshell stability (half-filled or full).

55. Which of the following shows an unexpected *decrease* in ionization energy across a period?

(A) Li → Be
(B) Be → B
(C) C → N
(D) F → Ne

View Answer

Correct Answer: (B) Be → B
Explanation: B begins filling the 2p orbital, which is higher in energy and easier to remove than a 2s electron in Be.

66. Why is the ionization energy of oxygen lower than that of nitrogen, despite oxygen having more protons?

(A) Oxygen is larger in atomic radius
(B) Oxygen’s electron is removed from a new shell
(C) Paired electrons in O’s 2p orbital cause extra repulsion
(D) Nitrogen forms stronger covalent bonds

View Answer

Correct Answer: (C) Paired electrons in O’s 2p orbital cause extra repulsion
Explanation: Oxygen’s 2p orbital has paired electrons, increasing repulsion and making ionization easier.

ap chemistry 2차 - unit 1

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