The order is 2 then 1 then 3..
OCh3 have +R and -I.....resonance effect operates on ortho and para position not on meta...therefore at meta due to -I electron density on carboxylate ion gets decreased which increases the acidity

Increasing order of acidity:
1. p - methoxybenzoic acid
2. m - methoxybenzoic acid
3. Benzoic acid

Explanation:

Introduction:
Acidity is a measure of the ability of a substance to donate a proton (H+) or accept an electron pair. The acidity of a compound is primarily determined by the stability of its conjugate base, which is formed after the loss of a proton. In general, the more stable the conjugate base, the stronger the acid.

1. p - Methoxybenzoic acid:
p - Methoxybenzoic acid (p-MBA) is an aromatic carboxylic acid in which a methoxy group (-OCH3) is attached to the benzene ring at the para position. The presence of the electron-donating methoxy group increases the electron density on the benzene ring, making it more acidic. This electron-donating effect destabilizes the conjugate base, making the acid more acidic. Therefore, p-MBA is the most acidic among the given compounds.

2. m - Methoxybenzoic acid:
m - Methoxybenzoic acid (m-MBA) is similar to p-MBA, but the methoxy group is attached to the benzene ring at the meta position. The electron-donating effect of the methoxy group is weaker at the meta position compared to the para position. As a result, the electron density on the benzene ring is slightly lower, making m-MBA less acidic than p-MBA.

3. Benzoic acid:
Benzoic acid is a simple aromatic carboxylic acid where a hydrogen atom is attached directly to the benzene ring. It does not have any electron-donating or electron-withdrawing groups attached to the ring. Therefore, it is less acidic compared to p-MBA and m-MBA.

Conclusion:
The increasing order of acidity is as follows: p - methoxybenzoic acid > m - methoxybenzoic acid > benzoic acid. The presence and position of the electron-donating methoxy group influence the acidity of these compounds.