The reagent that can be used to distinguished between methanoic acid and ethanoic acid is (a) Sodium carbonate solution (b) Ammonical silver nitrate solution (c) Phenolphthalein (d) Neutral ferric chloride solution

Tollens' test is a classical chemical reaction used to differentiate between aldehydes, which can be oxidized, and ketones, which cannot be easily oxidized. In this test, a solution of silver nitrate in ammonia, known as Tollen's reagent, is used to react with the substance in question. Aldehydes reduce the Ag(NH₃)₂⁺ complex ion to metallic silver, resulting in a distinctive shiny silver mirror coating on the inside of the test tube.

When you're specifically looking at carboxylic acids, it's important to note that only aldehyde-containing acids such as methanoic acid (HCOOH) will give a positive Tollens' test due to its reducing properties. In the context of distinguishing methanoic acid from ethanoic acid (CH₃COOH), which does not contain an aldehyde group, the Tollens' test becomes extremely useful. Methanoic acid reacts to form the silver mirror, while ethanoic acid does not, hence providing a clear distinction between the two.

Reducing agents are substances that donate electrons to another chemical species, thereby reducing it. They are integral in many chemical reactions, especially in redox processes where the transfer of electrons determines the direction and products of the reaction. A reducing agent itself becomes oxidized as it loses electrons.

In the context of the problem at hand, methanoic acid behaves as a reducing agent due to its ability to donate electrons to other compounds. This property is used in the Tollens' test, where methanoic acid donates electrons to the ammonical silver nitrate solution and reduces the silver ions to metallic silver, all the while being oxidized to carbon dioxide and water. Ethanoic acid, on the other hand, lacks this reducing capability which is why it does not show any reaction with Tollens' reagent.

Carboxylic acids are organic compounds characterized by the presence of a carboxyl group (COOH). This group is highly polar, making the acids generally higher in boiling point and more soluble in water compared to hydrocarbons of similar molecular weight.

One of the key chemical properties of carboxylic acids is their ability to participate in a wide variety of chemical reactions. They can act as acids, donating a proton to bases, or they can form esters in esterification reactions. Importantly, certain carboxylic acids like methanoic acid also exhibit reducing properties, distinguishing them from others such as ethanoic acid.

The reducing behavior of methanoic acid, in contrast to ethanoic acid, which lacks this property, is a significant feature that facilitates specific chemical tests like the Tollens' test for their distinction. The difference in reactivity of methanoic and ethanoic acids with a reagent like ammonical silver nitrate forms the crux of the distinction process.