Oxalic acid is used:
[This question has multiple correct options]
(A) For removing ink stains
(B) For the lab preparation of formic acid and allyl alcohol
(C) In making beverages
(D) As a mordant in dyeing and calico-painting

Hint: Oxalic acid is a dicarboxylic acid with molecular formula ${C_2}{H_2}{O_4}$. It has two nucleophilic oxygen atoms which can donate electrons in order to form metal complexes. Thus, oxalate ions can act as a chelating agent.

Complete Step-by-Step Solution:
We will first get some information about oxalic acid and then we will see its uses.
- Oxalic acid is a dicarboxylic acid with molecular formula ${C_2}{H_2}{O_4}$. It is generally available in its dihydrate form. It is the smallest dicarboxylic acid molecule. It is a white crystalline solid.
- The conjugate base of oxalic acid which is known as oxalate ion is a chelating agent for metals. It forms chelates with metals.
- It is used in removing the stains caused by rust and inks. It forms a complex with the iron in the rust. It also removes ink from the clothes. Thus, option (A) is correct.
- We can obtain formic acid from oxalic acid if we heat oxalic acid at ${110^ \circ }C$ with glycerol. It gives formic acid as a product. If we heat the mixture of formic acid and glycerol and at $200 - {210^ \circ }C$, then it will give allyl alcohol as a product. Thus, option (B) is also correct.
- Oxalic acid is not used in making beverages.
- Almost 25% of the oxalic acid produced is used as mordant in dyeing. It is also used in calico painting. Thus, option (D) is also correct.

Therefore, we can conclude that option (A), (B) and (D) are correct.

Note: Note that glycerine or glycerol is the reagent which is used to convert oxalic acid to formic acid and allyl alcohol. If we heat the solution around ${110^ \circ }C$ , then we obtain formic acid and if the mixture is heated more upto ${210^ \circ }C$, then allyl alcohol is obtained.