Question

Which one of the following compounds will not give aldol?
A) acetaldehyde
B) formaldehyde
C) pivaldehyde
D) crotonaldehyde
Which one of the following will give positive tollens test

Answer 1

Hint: All that you have to know is the concept of adol and tollens test, how to find it.
You must know which element has alpha hydrogen by this you can identify which element can undergo aldol condition. Also, you must know as the tollens test gives the positive only when aldehyde and hydroxy ketone is present.

Complete answer:
The correct option as per the compound will not give aldol is Formaldehyde and Pivaldehydethey do not undergo aldol condensation reaction because both formaldehyde and pivaldehyde does not contain alpha hydrogen atom.
Formaldehyde does not undergo aldol condensation, but acetaldehyde does.
Aldehydes having at least one alpha hydrogen which helps to undergo aldol condensation in the presence of a base to give alpha hydroxy aldehydes.
Therefore, acetaldehyde $C{H}_{3}COH$ has alpha hydrogen whereas formaldehyde $HCHO$ has no$\alpha -H$, so, the former can undergo aldol condensation.
Formaldehyde does not contain alpha hydrogen so it does not undergo aldol condensation.
An aldol condensation, to form a conjugated enone enolate ion, reacts with another carbonyl compound. In an aldol reaction, the two-part of the process occurs, which helps to form an dehydration reaction, and the aldol product, to form the final product it removes water. Either acids or bases can catalyze aldol condensation reaction though base catalysts are usually they are mostly preferred. To take place only with aldehydes this reaction was earlier supposed.
Formaldehyde and acetaldehyde both will give a positive tollens test. because the compound with alpha hydrogen will show the positive tollens test. Tollens test is generally given by compounds having an aldehydic group. It gives a white ppt of silver also to identify the alkynes it is more suitable for.

By seeing the both, option b correct answer.

Note:
Aldehyde and alcohol is an abbreviation of aldol. When the ketone or enolate of an aldehyde reacts at the alpha carbon with another molecule of carbonyl under the condition of basic or acidic to obtain ketone or$\beta$-hydroxy aldehyde, this type of reaction is known asAldol Reaction.
Tollens test only when aldehyde and alpha-hydroxy ketone is present gives a positive result.