Question

Assertion: Both o-hydroxybenzaldehyde and p-hydroxy benzaldehyde have the same molecular weight and show H-bonding.
Reason: Melting point of p-hydroxybenzaldehyde is more than o-hydroxybenzaldehyde.
A. Both assertion and reason are correct and reason is the correct explanation of the assertion.
B. Both assertion and reason are correct but reason is not the correct explanation of the assertion.
C. Assertion is correct but reason is incorrect.
D. Both assertion and reason are incorrect.

Answer 1

Hint:In the above question, some assertion o-hydroxybenzaldehyde and p-hydroxybenzaldehyde about is given. We are provided with the information about their melting point. We have to check which of the following options suits the best. The basic difference between o-hydroxybenzaldehyde and p-hydroxybenzaldehyde lies in the position of ${\text{ - OH}}$ group with respect to ${\text{ - CHO}}$ group which makes them differ in chemical characteristics as well.

Complete step-by-step answer:Both ortho-hydroxybenzaldehyde (o-hydroxybenzaldehyde) and para-hydroxy benzaldehyde (p-hydroxybenzaldehyde) are the isomers of hydroxyl benzaldehyde. And hence, the molecular weight of the two compounds are the same and both of them show H-bonding. So, the assertion is correct.
In o-hydroxybenzaldehyde, if the ${\text{ - CHO}}$ group is present at 1 location of the benzene ring then ${\text{ - OH}}$ group is present at 2 locations. Due to the presence of H-atoms closer to each other, they show intramolecular hydrogen bonding.
In p-hydroxybenzaldehyde, if the ${\text{ - CHO}}$ group is present at 1 location of the benzene ring then ${\text{ - OH}}$ group is present at 4 locations. Due to absence of H-atoms closer to each other, they show intermolecular hydrogen bonding.

Due to intermolecular hydrogen bonding or the bonding between adjacent molecules, the melting point of p-hydroxybenzaldehyde is more than o-benzaldehyde.
Since, both assertion and reason are correct but reason is not the correct explanation of the assertion.

b>Therefore, the correct option is option B.

Note:Although o-hydroxybenzaldehyde and p-hydroxy benzaldehyde have the same molecular mass and chemical formula, still they differ significantly due to difference in the type of their H-bonding. To answer any question related to ortho and para type question, answer with respect to intermolecular and intermolecular H-bonding.