Question

Select the correct order with respect to acid strength.

• A. \(m\text{-Cresol} \lt Phenol \lt m\text{-Nitrophenol} \lt p\text{-Nitrophenol}\)
• B. \(m\text{-Cresol} \lt Phenol \lt p\text{-Nitrophenol} \lt m\text{-Nitrophenol}\)
• C. \(m\text{-Cresol} \lt p\text{-Nitrophenol} \lt Phenol \lt m\text{-Nitrophenol}\)
• D. \(p\text{-Nitrophenol} \lt m\text{-Cresol} \lt Phenol \lt m\text{-Nitrophenol}\)

Hint:

For substituted phenols: \[ \text{Electron withdrawing group} \Rightarrow \text{Acidity increases} \] \[ \text{Electron donating group} \Rightarrow \text{Acidity decreases} \] The para nitro group increases acidity more effectively than the meta nitro group because resonance stabilization is possible.

Answer 1

The Correct Option is A

Step 1: Recall what controls phenol acidity.
A phenol is more acidic when the group on the ring pulls electrons away, stabilising the negative phenoxide ion. Electron-donating groups do the opposite and weaken the acid.

Step 2: Place m-Cresol.
The methyl group donates electrons (and there is no resonance help in the meta spot for opposite effect), so m-cresol is less acidic than plain phenol. So m-Cresol is weakest.

Step 3: Place Phenol.
Plain phenol sits next, more acidic than m-cresol but weaker than the nitro phenols.

Step 4: Compare the nitrophenols.
The $-NO_2$ group withdraws electrons and makes the acid stronger. A nitro at para can stabilise the charge by resonance, while at meta it works mostly by induction.

Step 5: Order the two nitro compounds.
By resonance, p-nitrophenol is the more acidic of the two, with m-nitrophenol just below it.

Step 6: Write the full order.
So acid strength rises as m-Cresol $\lt$ Phenol $\lt$ m-Nitrophenol $\lt$ p-Nitrophenol, the first option.
\[ \boxed{m\text{-Cresol} \lt \text{Phenol} \lt m\text{-Nitrophenol} \lt p\text{-Nitrophenol}} \]