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Exceptions to the octet rule (incomplete, odd-electron, expanded octet)

This type of question, asked 6 times: 25 Jun 2022, 29 Jul 2022, 29 Jan 2023, 8 Apr 2024, 23 Jan 2025, 6 Apr 2026 S2. All 6 questions below, oldest first.

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  1. Question 1

    25 Jun 2022

    35
    Number of electron deficient molecules among the following PH3, B2H6,CCl4,NH3,LiHPH_{3},{\text{ }B}_{2}H_{6},CCl_{4},NH_{3},LiH and BCl3BCl_{3} is

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  2. Question 2

    29 Jul 2022

    31
    Which of the following pair of molecules contain odd electron molecule and an expanded octet molecule?

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  3. Question 3

    29 Jan 2023

    57
    The number of molecules or ions from the following, which do not have odd number of electrons are (A) NO2NO_{2} (B) ICl4−ICl_{4}^{-} (C) BrF3BrF_{3} (D) ClO2ClO_{2} (E) NO2+NO_{2}^{+} (F) NO
  4. Question 4

    8 Apr 2024

    56
    Number of molecules from the following which are exceptions to octet rule is ______ . CO2,NO2,H2SO4,BF3,CH4,SiF4,ClO2,PCl5CO_{2},NO_{2},H_{2}SO_{4},BF_{3},CH_{4},SiF_{4},ClO_{2},PCl_{5}, BeF2,C2H6,CHCl3,CBr4BeF_{2},C_{2}H_{6},CHCl_{3},CBr_{4}
  5. Question 5

    23 Jan 2025

    44
    Match the LIST-I with LIST-II
    LIST-I (Classification of molecules based on octet rule)LIST-II (Example)
    (A)Molecules obeying octet rule(I)
    NO,NO2NO,NO_{2}
    (B)Molecules with incomplete octet(II)
    BCl3,AlCl3BCl_{3},AlCl_{3}
    (C)Molecules with incomplete octet with odd electron(III)
    H2SO4,PCl5H_{2}SO_{4},PCl_{5}
    (D)Molecules with expanded octet(IV)
    CCl4,CO2CCl_{4},CO_{2}
    Choose the correct answer from the options given below :

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  6. Question 6

    6 Apr 2026 S2

    28
    Given below are two statements: Statement I: The number of compounds among SO2,SO3,SF4,SF6{SO}_{2},{SO}_{3},{SF}_{4},{SF}_{6} and H2 SH_{2}\text{ }S in which sulphur does not obey the Octet rule is 3 . Statement II : Among [H2O,ClF3,SF4],[NH3\left\lbrack H_{2}O,{ClF}_{3},{SF}_{4} \right\rbrack,\left\lbrack {NH}_{3} \right.,  BrF5,SF4], [BrF5, ClF3, XeF4]\left. \ {BrF}_{5},{SF}_{4} \right\rbrack,\ \left\lbrack {BrF}_{5},\ {ClF}_{3},\ {XeF}_{4} \right\rbrack and  [XeF4\ \left\lbrack {XeF}_{4} \right.,  ClF3,H2O]\left. \ {ClF}_{3},H_{2}O \right\rbrack, the number of sets in which all the molecules have one lone pair of electrons on the central atom is 1 . In the light of the above statements, choose the correct answer from the options given below :

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