Kossel-Lewis approach; octet rule and its limitations — NEET & JEE Questions

Question 1 · difficulty L1 · recall

The octet rule states that many main-group atoms tend to gain, lose or share electrons to achieve

• A. eight electrons in their valence shell
• B. eight protons in the nucleus
• C. a completely empty valence shell
• D. exactly two total electrons in every case

Question 2 · difficulty L2 · understanding

The formal charges on the atoms marked as (1) to (4) in the Lewis representation of $\mathrm{HNO}_3$ molecule respectively are

• A. $0,0,-1,+1$
• B. $0,-1,0,+1$
• C. $0,+1,0,-1$
• D. $+1,0,0,-1$

Question 3 · difficulty L2 · understanding

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) $\mathrm{NO}, \mathrm{NO}_2$ (B) Molecules with incomplete octet (II) $\mathrm{BCl}_3, \mathrm{AlCl}_3$ (C) Molecules with incomplete octet with odd electron (III) $\mathrm{H}_2 \mathrm{SO}_4, \mathrm{PCl}_5$ (D) Molecules with expanded octet (IV) $\mathrm{CCl}_4, \mathrm{CO}_2$ Choose the correct answer from the options given below:

• A. A-IV, B-I, C-III, D-II
• B. A-II, B-IV, C-III, D-I
• C. A-IV, B-II, C-I, D-III
• D. A-III, B-II, C-I, D-IV

Question 4 · difficulty L2 · understanding

According to Lewis theory, the total number of $\sigma$ bond-pairs and lone pair of electrons around the central atom of $\mathrm{XeO}_6{ }^{4-}$ ion is $\_\_\_\_$ .

Question 5 · difficulty L2 · understanding

Total number of non-bonded electrons present in NO 2 $-$ ion based on Lewis theory is ______.

Question 6 · difficulty L2 · understanding

Number of molecules from the following which are exceptions to octet rule is _________. $$\mathrm{CO}_2, \mathrm{NO}_2, \mathrm{H}_2 \mathrm{SO}_4, \mathrm{BF}_3, \mathrm{CH}_4, \mathrm{SiF}_4, \mathrm{ClO}_2, \mathrm{PCl}_5, \mathrm{BeF}_2, \mathrm{C}_2 \mathrm{H}_6, \mathrm{CHCl}_3, \mathrm{CBr}_4$$

Question 7 · difficulty L2 · understanding

In the lewis dot structure for $$\mathrm{NO}_2^{-}$$, total number of valence electrons around nitrogen is _________.

Question 8 · difficulty L2 · understanding

The number of molecules or ions from the following, which do not have odd number of electrons are _________. (A) NO$$_2$$ (B) ICl$$_4^ -$$ (C) BrF$$_3$$ (D) ClO$$_2$$ (E) NO$$_2^ +$$ (F) NO

Question 9 · difficulty L3 · understanding

Given below are two statements : Statement I : The number of compounds among $\mathrm{SO}_2, \mathrm{SO}_3, \mathrm{SF}_4, \mathrm{SF}_6$ and $\mathrm{H}_2 \mathrm{~S}$ in which sulphur does not obey the Octet rule is 3 . Statement II : Among $\left[\mathrm{H}_2 \mathrm{O}, \mathrm{ClF}_3, \mathrm{SF}_4\right],\left[\mathrm{NH}_3, \mathrm{BrF}_5, \mathrm{SF}_4\right],\left[\mathrm{BrF}_5, \mathrm{ClF}_3, \mathrm{XeF}_4\right]$ and [ $\mathrm{XeF}_4, \mathrm{ClF}_3, \mathrm{H}_2 \mathrm{O}$ ], 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 :

• A. Both Statement I and Statement II are true
• B. Both Statement I and Statement II are false
• C. Statement I is true but Statement II is false
• D. Statement I is false but Statement II is true

Question 10 · difficulty L3 · understanding

The pairs among $\mathrm{A}=\left[\mathrm{SO}_3^{2-}, \mathrm{CO}_3^{2-}\right], \mathrm{B}=\left[\mathrm{O}_2^{2-}, \mathrm{F}_2\right], \mathrm{C}=\left[\mathrm{CN}^{-}, \mathrm{CO}\right], \mathrm{D}=\left[\mathrm{NH}_3, \mathrm{H}_3 \mathrm{O}^{+}\right]$and $\mathrm{E}=\left[\mathrm{MnO}_4^{2-}, \mathrm{CrO}_4^{2-}\right]$ that do not have similar Lewis dot structure are

• A. A, B and E
• B. A and E
• C. B, C and D
• D. C and D