$C{{H}_{3}}CHO$ and $C{{H}_{3}}COC{{H}_{3}}$ cannot be extinguished by:
[A] Fehling solution
[B] Grignard reagent
[C] Schiff’s reagent
[D] Tollen’s reagent

Hint: To answer this you must know which groups are the following reagents used to identify. You should know that the given compounds contain –CO and –CHO groups. Find out the reagents that we use to distinguish between them and the one that does not react with either of them will be the correct answer.

Complete step by step solution: We know that $C{{H}_{3}}CHO$ is an aldehyde and its name is acetaldehyde and $C{{H}_{3}}COC{{H}_{3}}$ is acetone and it is a ketone.
Firstly discuss the reagents given to us in order to find out the appropriate reagent to distinguish between $C{{H}_{3}}CHO$ and $C{{H}_{3}}COC{{H}_{3}}$.
Firstly, we have a Fehling solution. This solution contains two separate solutions named Fehling solution A and Fehling solution B. Fehling solution A is an aqueous solution of copper sulphate and Fehling solution B is a solution of potassium sodium tartrate. This solution is used to differentiate ketones and carbohydrates. Next we have Grignard reagent. This reagent is magnesium containing a chemical compound with the formula- R-Mg-X. R can be any alkyl group and X stands for halide. The most common example is $C{{H}_{3}}MgCl$. This reagent reacts rapidly with acidic hydrogen like in alcohols and forms water and alkanes.
Then we have Schiff’s reagent. It is an organic dye. It is a mixture of sulphurous acid and fuschsine (also known as rosaniline hydrochloride) with the chemical formula ${{C}_{20}}{{H}_{20}}{{N}_{3}}\cdot HCl$. It has a magenta red colour which is discoloured by sulphur dioxide. This test is used to distinguish between aldehydes and ketones. Ketones have no effect on this reagent whereas aldehydes restore the red colour.
And lastly, we have Tollen’s reagent. Tollen’s test is also known as the silver mirror test. We use it to determine the presence of aldehyde and aromatic aldehydes. It is also used for the detection of some alpha-hydroxy ketones which undergo tautomerization to form an aldehyde. We can understand from the above discussion that we can use Fehling solution, Tollen’s reagent and Schiff's reagent to distinguish between aldehydes and ketones as they are only given by ketones. But, we cannot use Grignard reagent for this purpose.

Therefore, the correct answer is option [B] Grignard reagent

Note: Aldehydes are very similar to ketones. The only difference is ketones have a ‘R’ group instead of the hydrogen atom. Aldehydes with maximum 4 carbons (as well as ketones) are soluble in water due to the possibility of hydrogen bonding. Higher aldehydes (and ketones) do not dissolve in water. Aldehydes undergo reactions similar to ketones like halogenation, oxidation, reduction etc.