MCQ
Which of the following pairs of substances illustrate the law of multiple proportions
- ✓$CO$ and $CO_2$
- B${H_2}O$ and $ {D_2}O$
- C$NaCl$ and $NaBr$
- D$MgO$ and $Mg{(OH)_2}$

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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. $\mathrm{F}$ is the most electronegative element.
In the light of the above statements, choose the correct answer from the options given below: