Answer:
phenol
Explanation:
The pKa may be regarded as a measure of how tightly a proton is held by the conjugate Brownstead-Lowry acid.
The lower the value of the pKa, the more easily the proton may be lost. The higher the pKa the less easily the proton is lost. The pKa may sometimes be so low that it is even a negative number!
pKa is a masure of acid strength. While strong acids have a smaller pKa, weak acids have a larger pKa. From the foregoing, phenol having the smallest pKa among all compounds listed, will be almost completely deprotonated by NaOH.
