Question

Which of the following is most acidic?
A.
B.
C.
D.

Answer 1

As we know that the acids and bases are the chemical compounds. When they react together, there is a formation of salt and water. The acid is a chemical substance which contains hydrogen and it donates the protons to another substance. And the base is a chemical substance which accepts the hydrogen ion. The acidic substances are sour in taste and it turns blue litmus to red. The base has a bitter taste and it turns red litmus to blue.

Complete answer:
The phenol is not most acidic from the given compound. Hence, option (A) is incorrect.
The $2 -$ methoxy phenol is not most acidic from the given compounds. Hence, option (B) is incorrect.
Among the given compounds $4 -$ methoxy phenol is not the most acidic compound. Hence, option (C) is incorrect.
Among the given options, $3 -$ methoxy phenol is the most acidic compound. Because, the methoxy group is inductive withdrawing and they are mesomeric donating. We know that the mesmeric effect will override the inductive effect. But the mesomeric effect is only valid when the substituent is attached on the para position and the ortho position.
And the addition of an electron donating group to the phenol ring will affect the acidity. Because, the acidity will decrease when an electron donating group is attached to the phenol ring. But the acidity will increase when the electron withdrawing group is attached to the phenol ring. Thus, we can say that the meta- methoxy phenol is more acidic than the others.

Hence, option (D) is correct.

Note:
We need to know that the acidity of the compound increases when an electron withdrawing group is present in that compound. The inductive effect will affect the acidity and basicity of a compound. Because, when the number of negative inductive groups is increasing, there is a chance to increase the acidity. And if the positive inductive group is present, there is a chance to increase the basicity.