Question: 87. Identify the correct orders against the property mentioned
A. \mathrm{H}_{2} \mathrm{O}>\mathrm{NH}_{3}>\mathrm{CHCl}_{3} – dipole moment
B. \mathrm{XeF}_{4}>\mathrm{XeO}_{3}>\mathrm{XeF}_{2}- number of lone pairs on central atom
C. \mathrm{O}-\mathrm{H}>\mathrm{C}-\mathrm{H}>\mathrm{N}-\mathrm{O}- bond length
D. \mathrm{N}_{2}>\mathrm{O}_{2}>\mathrm{H}_{2}- bond enthalpy
Choose the correct answer from the options given below:
(1) A, D only
(2) B, D only
(3) A, C only
(4) B, C only
Answer: Option (1)
Explanation:
For statement A, dipole moment depends on molecular geometry and bond polarity.
\mathrm{H}_{2}\mathrm{O} has a bent structure and highly polar \mathrm{O}-\mathrm{H} bonds, giving the highest dipole moment.
\mathrm{NH}_{3} is also polar with a pyramidal shape but has a lower dipole moment than water.
\mathrm{CHCl}_{3} has partial cancellation of bond dipoles, resulting in a smaller dipole moment.
Thus, order A is correct.
For statement B, the number of lone pairs on xenon are:
\mathrm{XeF}_{2} has 3 lone pairs,
\mathrm{XeF}_{4} has 2 lone pairs,
and \mathrm{XeO}_{3} has 1 lone pair.
The correct order should be
\mathrm{XeF}_{2}>\mathrm{XeF}_{4}>\mathrm{XeO}_{3}.
Hence, statement B is incorrect.
For statement C, bond length increases with decrease in bond order and increase in atomic size.
The correct bond length order is
\mathrm{N}-\mathrm{O}>\mathrm{C}-\mathrm{H}>\mathrm{O}-\mathrm{H}.
Given order is incorrect, so statement C is false.
For statement D, bond enthalpy depends on bond order.
\mathrm{N}_{2} has a triple bond,
\mathrm{O}_{2} has a double bond,
and \mathrm{H}_{2} has a single bond.
Thus, bond enthalpy decreases in the order
\mathrm{N}_{2}>\mathrm{O}_{2}>\mathrm{H}_{2}.
Hence, statement D is correct.
Therefore, only statements A and D are correct.