1.
Give the correct order of acidic strength of the following compounds:

(a) NO2–CH2–COOH\text{NO}_2\text{–CH}_2\text{–COOH}
(b) F–CH2–COOH\text{F–CH}_2\text{–COOH}
(c) Ph–CH2–COOH\text{Ph–CH}_2\text{–COOH}
(d) CH3–CH2–COOH\text{CH}_3\text{–CH}_2\text{–COOH}