Given below are two statements : one is labelled as Assertion (A) and the other is labelled as Reason (R). Assertion (A) : \(\mathrm{NH}_{3}\) and \(\mathrm{NF}_{3}\) molecule have pyramidal shape with a lone pair of electrons on nitrogen atom. The resultant dipole moment of \(\mathrm{NH}_{3}\) is greater than that of \(\mathrm{NF}_{3}\). Reason (R): In \(\mathrm{NH}_{3}\), the orbital dipole due to lone pair is in the same direction as the resultant dipole moment of the \(\mathrm{N}-\mathrm{H}\) bonds. F is the most electronegative element. In the light of the above statements, choose the correct answer from the options given below:

(A) Both (A) and (R) are true and (R) is the correct explanation of (A)

(B) (A) is false but (R) is true

(C) (A) is true but (R) is false

(D) Both (A) and (R) are true but (R) is NOT the correct explanation of (A)

Chemical Bonding and Molecular Structure — JEE Main · 2024 · 05 Apr 2024 · Shift 2 Question with Solution

Given below are two statements : one is labelled as Assertion (A) and the other is labelled as Reason (R).

Assertion (A) :

NH_{3}

and

NF_{3}

molecule have pyramidal shape with a lone pair of electrons on nitrogen atom. The resultant dipole moment of

NH_{3}

is greater than that of

NF_{3}

.

Reason (R): In

NH_{3}

, the orbital dipole due to lone pair is in the same direction as the resultant dipole moment of the

N - H

bonds. F is the most electronegative element.

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

(A)Both (A) and (R) are true and (R) is the correct explanation of (A)✓ Correct
(B)(A) is false but (R) is true
(C)(A) is true but (R) is false
(D)Both (A) and (R) are true but (R) is NOT the correct explanation of (A)

Answer: (A)

Solution

N H_{3}

, the lone pair on nitrogen and the resultant of the three

N

–

H

bond dipoles both point away from the hydrogens, toward and beyond N, so they reinforce each other, giving a comparatively large net dipole moment (

\approx 1.47

D).
In

N F_{3}

, the highly electronegative fluorine atoms pull electron density (and hence the bond-dipole resultant) toward themselves, i.e. away from N, so the bond-dipole resultant now opposes the lone-pair dipole and partly cancels it, giving a much smaller net moment (

\approx 0.24

D). So the Assertion (net dipole of

N H_{3}

greater than

N F_{3}

) is true, and the Reason correctly identifies why — the lone-pair dipole adds to the bond-dipole resultant in

N H_{3}

but opposes it in

N F_{3}

because F is strongly electronegative.

JEE Main · 2024 · 05 Apr 2024 · Shift 2 · Single correct option

JEE Main · 2024 · 05 Apr 2024 · Shift 2 · Chemical Bonding and Molecular Structure

Solution

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