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Modern periodic law and present periodic table: NEET MCQs with answers

69 questions on this topic of Classification of Elements and Periodicity in Properties (NEET 2027 syllabus). Here are 12; tap one to see its answer and explanation.

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easy

1. Which of the following statements is correct regarding the modern periodic law and the long form of the periodic table?

  1. The physical and chemical properties of the elements are periodic functions of their atomic weights.
  2. The law was originally formulated by Henry Moseley based on his experiments on the diffraction of α-particles.
  3. The modern periodic law states that the properties of the elements are periodic functions of their atomic numbers.
  4. The long form of the periodic table was developed primarily by John Newlands based on the law of octaves.
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Answer: (C) The modern periodic law states that the properties of the elements are periodic functions of their atomic numbers.

The modern periodic law states that the physical and chemical properties of the elements are periodic functions of their atomic numbers. It was established following Moseley's work with characteristic X-ray spectra of elements, not α-particle diffraction. Mendeleev's law was based on atomic weights, while Newlands formulated the law of octaves.

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2. The element with atomic number 3 belongs to:

  1. Period 3, Group 1
  2. Period 2, Group 1
  3. Period 3, Group 2
  4. Period 2, Group 2
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Answer: (B) Period 2, Group 1

The outermost shell of the element with Z = 3 is n = 2, and counting its s, d and p valence electrons across groups 1 to 18 places it in group 1: Period 2, Group 1.

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3. An newly synthesized element has atomic number Z = 117. Which of the following sets correctly lists its IUPAC temporary name, group number, and block?

  1. Ununseptium, Group 15, p-block
  2. Ununseptium, Group 17, p-block
  3. Ununhexium, Group 16, p-block
  4. Ununoctium, Group 17, d-block
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Answer: (B) Ununseptium, Group 17, p-block

For Z = 117, 1='un', 1='un', 7='sept', ending in 'ium', giving Ununseptium (Uus). The electronic configuration is [Rn] 5f¹⁴ 6d¹⁰ 7s² 7p⁵. The last electron enters the 7p subshell (p-block) and the group number is 10 + 2 + 5 = 17 (a halogen, officially Tennessine).

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4. An element has the valence shell electronic configuration 4f¹⁴ 5d¹ 6s². To which group and period of the modern periodic table does it belong?

  1. Group 3, Period 6
  2. Group 4, Period 6
  3. Group 17, Period 6
  4. Group 3, Period 5
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Answer: (A) Group 3, Period 6

The maximum principal quantum number is n = 6, so it belongs to period 6. The element is Lutetium (Z = 71), which is classified under Group 3 as the terminating member of the lanthanoid series.

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5. Given below are two statements: Statement I: The first period of the modern periodic table contains only 2 elements because the first energy level (n = 1) can accommodate a maximum of 2 electrons. Statement II: The 3rd period of the modern periodic table contains 18 elements because the 3d-subshell is filled in this period. In the light of the above statements, choose the most appropriate answer from the options given below:

  1. Both Statement I and Statement II are correct
  2. Statement I is correct but Statement II is incorrect
  3. Statement I is incorrect but Statement II is correct
  4. Both Statement I and Statement II are incorrect
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Answer: (B) Statement I is correct but Statement II is incorrect

Statement I is correct because for n = 1, only the 1s subshell exists, holding 2 electrons. Statement II is incorrect because the 3rd period contains only 8 elements (from Na to Ar), corresponding to the filling of 3s and 3p orbitals; the 3d subshell is filled in the 4th period.

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6. Match List-I (IUPAC Systematic Name) with List-II (Official IUPAC Name): List-I: (A) Unnilquadium (B) Unnilpentium (C) Unnilhexium (D) Unnilseptium List-II: (I) Seaborgium (II) Bohrium (III) Rutherfordium (IV) Dubnium Choose the correct answer from the options given below:

  1. (A)-(IV), (B)-(III), (C)-(I), (D)-(II)
  2. (A)-(III), (B)-(IV), (C)-(I), (D)-(II)
  3. (A)-(III), (B)-(IV), (C)-(II), (D)-(I)
  4. (A)-(I), (B)-(II), (C)-(III), (D)-(IV)
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Answer: (B) (A)-(III), (B)-(IV), (C)-(I), (D)-(II)

Unnilquadium (Z = 104) is Rutherfordium (III); Unnilpentium (Z = 105) is Dubnium (IV); Unnilhexium (Z = 106) is Seaborgium (I); Unnilseptium (Z = 107) is Bohrium (II). Hence, (A)-(III), (B)-(IV), (C)-(I), (D)-(II).

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7. The element with atomic number 30 belongs to:

  1. Period 4, Group 12
  2. Period 4, Group 11
  3. Period 3, Group 12
  4. Period 4, Group 13
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Answer: (A) Period 4, Group 12

The outermost shell of the element with Z = 30 is n = 4, and counting its s, d and p valence electrons across groups 1 to 18 places it in group 12: Period 4, Group 12.

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8. Which of the following electronic configurations corresponds to a noble gas element placed in period 7?

  1. [Rn] 5f¹⁴ 6d¹⁰ 7s²
  2. [Xe] 4f¹⁴ 5d¹⁰ 6s² 6p⁶
  3. [Rn] 6d¹⁰ 7s² 7p⁶
  4. [Rn] 5f¹⁴ 6d¹⁰ 7s² 7p⁶
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Answer: (D) [Rn] 5f¹⁴ 6d¹⁰ 7s² 7p⁶

The period 7 noble gas is Oganesson (Z = 118). Its electronic configuration is [Rn] 5f¹⁴ 6d¹⁰ 7s² 7p⁶, completely filling all available orbitals in this period.

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9. An element belongs to period 6 and group 12 of the modern periodic table. What is its atomic number and valence electronic configuration?

  1. Z = 48, 4d¹⁰ 5s²
  2. Z = 80, 4f¹⁴ 5d¹⁰ 6s²
  3. Z = 70, 4f¹⁴ 6s²
  4. Z = 112, 5f¹⁴ 6d¹⁰ 7s²
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Answer: (B) Z = 80, 4f¹⁴ 5d¹⁰ 6s²

Period 6 ends with radon (Z = 86). Group 12 in period 6 is Mercury (Hg), with atomic number Z = 80. Its ground state electronic configuration is [Xe] 4f¹⁴ 5d¹⁰ 6s².

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10. Given below are two statements: one is labelled as Assertion (A) and the other is labelled as Reason (R). Assertion (A): Helium has the electronic configuration 1s² and is placed in Group 18 with noble gases rather than in Group 2 with alkaline earth metals. Reason (R): Helium has a completely filled valence shell, exhibiting characteristic inert chemical behavior similar to other noble gases. In the light of the above statements, choose the correct answer from the options given below:

  1. Both (A) and (R) are true and (R) is the correct explanation of (A)
  2. Both (A) and (R) are true but (R) is not the correct explanation of (A)
  3. (A) is true but (R) is false
  4. (A) is false but (R) is true
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Answer: (A) Both (A) and (R) are true and (R) is the correct explanation of (A)

Though Helium has an s² configuration characteristic of s-block elements, its valence shell (n = 1) is completely full (duplet), giving it chemical inertness identical to Group 18 noble gases, which is why it is placed in Group 18.

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11. The element with atomic number 12 belongs to:

  1. Period 3, Group 2
  2. Period 4, Group 1
  3. Period 4, Group 2
  4. Period 3, Group 1
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Answer: (A) Period 3, Group 2

The outermost shell of the element with Z = 12 is n = 3, and counting its s, d and p valence electrons across groups 1 to 18 places it in group 2: Period 3, Group 2.

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12. An element has atomic number Z = 46. To which group and block does this element belong?

  1. Group 8, d-block
  2. Group 10, d-block
  3. Group 12, d-block
  4. Group 2, s-block
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Answer: (B) Group 10, d-block

Element Z = 46 is Palladium (Pd). Its ground-state configuration is [Kr] 4d¹⁰ 5s⁰. It belongs to period 5, d-block, and group 10 (since 10 electrons reside in the valence/penultimate d subshell: group = 10 + 0 = 10).

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