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Classification of Elements and Periodicity in Properties

JEE Main 2026 (Online) 24th January Evening ShiftMCQMedium📈 Topic in 32% papers+4−1
Ques. 1JEE Main 2026, 24 January (Evening Shift)

The correct order of C, N, O and F in terms of second ionisation potential is

  1. C < N < F < O
  2. C < F < N < O
  3. F < N < C < O
  4. C < O < N < F

Answer

(1) C < N < F < O

Solution

Second ionisation removes an electron from the unipositive ion:

C+: 2s2 2p1; N+: 2s2 2p2; O+: 2s2 2p3; F+: 2s2 2p4

Across the period IE2 rises with nuclear charge, but O+ has a stable half-filled 2p3 configuration, so removing an electron from it is harder than from F+ (2p4).

IE2 ( kJ mol-1): C 2353, N 2856, O 3388, F 3374

C < N < F < O

Answer: (1)

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Ques. 2JEE Main 2026, 23 January (Morning Shift)

The correct trend in the first ionization enthalpies of the elements in the 3rd period of periodic table is :

  1. Si < S < Al < P < Cl
  2. Al < Si < S < P < Cl
  3. S < Si < Al < P < Cl
  4. Al < S < P < Si < Cl
Ques. 3JEE Main 2026, 23 January (Evening Shift)

Given below are two statements : In the light of the above statements, choose the correct answer from the options given below :

  1. Statement I is true but Statement II is false
  2. Statement I is false but Statement II is true
  3. Both Statement I and Statement II are true
  4. Both Statement I and Statement II are false
Ques. 4JEE Main 2026, 22 January (Morning Shift)

A 'p'-block element (E) and hydrogen form a binary cation (EHx)+, while EH3 on treatment with K2HgI4 in alkaline medium gives a precipitate of basic mercury(II) amido-iodine. Given below are first ionisation enthalpy values ( kJ mol-1) for first element each from group 13, 14, 15 and 16. Identify the correct first ionisation enthalpy value for element E.

  1. 1402
  2. 1086
  3. 801
  4. 1312
Ques. 5JEE Main 2026, 22 January (Evening Shift)

Given below are two statements : In the light of the above statements, choose the correct answer from the options given below :

  1. Both Statement I and Statement II are false
  2. Statement I is false but Statement II is true
  3. Statement I is true but Statement II is false
  4. Both Statement I and Statement II are true
Ques. 6JEE Main 2026, 21 January (Morning Shift)

Which of the following represents the correct trend for the mentioned property? Choose the correct answer from the options given below :

  1. B and C only
  2. A, B and D only
  3. A and B only
  4. A, B, C and D
Ques. 7JEE Main 2026, 21 January (Evening Shift)

Given below are two statements : In the light of the above statements, choose the correct answer from the options given below :

  1. Statement I is true but Statement II is false
  2. Both Statement I and Statement II are true
  3. Statement I is false but Statement II is true
  4. Both Statement I and Statement II are false
Ques. 8JEE Main 2025, 8 April (Evening Shift)

The atomic number of the element from the following with lowest 1st ionisation enthalpy is :

  1. 32
  2. 35
  3. 19
  4. 87
Ques. 9JEE Main 2025, 7 April (Evening Shift)

Choose the incorrect trend in the atomic radii (r) of the elements.

  1. rRb < rCs
  2. rAt < rCs
  3. rBr < rK
  4. rMg < rAl
Ques. 10JEE Main 2025, 3 April (Morning Shift)

Which of the following statements are correct? Choose the correct answer from the options given below:

  1. A, C and D Only
  2. B and C Only
  3. B and D Only
  4. B, C and E Only
Ques. 11JEE Main 2025, 3 April (Evening Shift)

Match the LIST-I with LIST-II Choose the correct answer from the options given below:

  1. A-IV, B-I, C-II, D-III
  2. A-IV, B-III, C-I, D-II
  3. A-III, B-I, C-IV, D-II
  4. A-II, B-III, C-IV, D-I

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