Q. 21

[admin]

Yes, you are correct that a carboxylic acid has an acidic hydrogen. However, from the question, all that we can conclude is that compound X lost a proton and is therefore an acid. Do we know what kind of acid it is? Carboxylic acids are the most common organic acid but there are many other options: sulfonic acids are actually more acidic than carboxylic acids, then there are weaker acids with functional groups like -OH, -SH, -enol, etc.

In other words, answer choice B is the best answer because it is the one thing that we can be sure of.

[dnpgr16513]

I don't understand why this answer isn't D. Aldehydes only have 1 type of proton, so in a reaction, the observance of the disappearance of a hydrogen wouldn't signify that it was an aldehyde?

Thanks.

[calena7178147]

Answer B is correct. Aldehydes do not all have only one type of protons. In particular when the carbon chain is long you have also protons attached to the carbon. Aldehydes have the following structure of RCOH. In addition, an acidic proton is lost with D2O replacement as stated and so B makes the most sense.