Question

Given below are two statements: one is labelled as assertion $\mathrm{A}$and the other is labelled as reason $\mathrm{R}$.

Assertion $\mathrm{A}$:Dipole-dipole interactions are the only non-covalent interactions, resulting in hydrogen bond formation.

Reason $\mathrm{R}$: Fluorine is the most electronegative element and hydrogen bonds in $\mathrm{HF}$ are symmetrical

In the light of the above statements, choose the most appropriate answer from the options given below:

• A. $\mathrm{A}$is false but $\mathrm{R}$ is true
• B. Both $\mathrm{A}$ and $\mathrm{R}$ are true and $\mathrm{R}$ is the correct explanation of $\mathrm{A}$
• C. $\mathrm{A}$ is true but $\mathrm{R}$ is false
• D. Both $\mathrm{A}$and $\mathrm{R}$ is not the the correct explanation of $\mathrm{A}$

Answer 1

The correct option is A

$\mathrm{A}$is false but $\mathrm{R}$ is true

Answer: (A)

Explanation for correct option:

$\mathrm{H}-$bonding is the bonding interaction between highly electronegative element such as $\mathrm{F},\mathrm{O}$ and $\mathrm{N}$ with $\mathrm{H}$-atom.

$\mathrm{F}$ is most electronegative element and anhydrous $\mathrm{HF}$ in solid phase has symmetrical hydrogen bonding . The strongest $\mathrm{H}-\mathrm{bonds}$ are formed by $\mathrm{F}-$atoms . Some hydrogen bonding also occurs in the gas, which consists of a mixture of cyclic ${\left(\mathrm{HF}\right)}_6$ polymers , dimeric ${\left(\mathrm{HF}\right)}_2$, and monomeric $\mathrm{HF}$.

Explanation for incorrect option:

Dipole- dipole are responsible for the interaction with two opposite charges irrespective of electronegativity and atomic size. While Hydrogen bonding is the special case of dipole dipole interaction where negative dipole must be highly electronegative element. Hence Assertion A is false.

Hence option (A) is correct option.