Write about $(a)$ Tollen's Test and $(b)$ Fehling solution. $OR$ Write the oxidation reaction of only aldehyde. $OR$ Write tests which are utilized to differentiate aldehydes and ketones.

(A) Explanation: Oxidation of aldehyde compounds is easier than that of ketones. In this oxidation of aldehyde compounds,the conversion of $C-H$ to $C-OH$ is easily carried out. Due to this reason,the oxidation of aldehyde to acid is done with mild oxidizing agents like $Ag^{+}$,$Cu^{2+}$,etc.
Oxidation of aldehyde can be done by $(i)$ Tollen's reagent and $(ii)$ Fehling reagent,but the oxidation of ketone cannot be done under these conditions. So,for this reason,the mild oxidizing agents given below are used to distinguish aldehydes from ketones.
$(a)$ Tollen's test: On warming an aldehyde with freshly prepared ammoniacal silver nitrate solution (Tollen's reagent),a bright silver mirror is produced due to the formation of silver metal. The aldehydes are oxidized to the corresponding carboxylate anion. The reaction occurs in an alkaline medium.
Procedure: When aldehyde compounds are heated with Tollen's reagent in a test tube,it gives silver metal,which produces a layer on the test tube inner wall and gives a silver mirror. In this reaction,the aldehyde $(-CHO)$ group is oxidized into a negative ion,carboxylate $(-COO^{-})$,while $Ag^{+}$ is reduced to $Ag$.
This Tollen's test is also known as the silver mirror test. This test is only given by aldehydes; ketones do not give this test.
$(b)$ Fehling Test: This test is only given by aliphatic aldehydes,but ketones do not give this test.
Fehling solution: Fehling solution $A$ and Fehling solution $B$ are mixed in equal proportions.
Fehling solution $A$: It is a solution of copper sulphate $(CuSO_{4}$ solution$)$.
Fehling solution $B$: It is an alkaline solution of sodium potassium tartrate (Rochelle salt).