Question

An example of vat dye is:
This question has multiple correct options
A. Indigo
B. Alizarin
C. Malachite green
D. Martius yellow

Answer 1

Vat dyeing is a process of dyeing and printing on cotton and cellulosic fibers and is classified such as it is done in a vat or a bucket. These dyes are generally insoluble in water.

Complete solution:
The vat dyes are named such because of the way they are applied , that is in a bucket or a vat. These dyes are very much important for the cotton dyeing industry, most vat dyes which require a reducing agent to solubilize them, are less suitable than fiber‐reactive dyes.
Indigo is an original vat dye . Earlier it was obtained from plants but it is produced synthetically also .
Alizarin also known as Mordant Red is an organic compound with formula $\left( {{C_{14}}{H_8}{O_4}} \right)$ that is been used as a red dye in the textile industry from many years is a type of vat dye
Malachite green is an organic compound that is used as a dyestuff and controversially as an antimicrobial in aquaculture. It is traditionally used as a dye for materials such as silk, leather, and paper.
Martius yellow is an organic compound which was used to protect wool from moth in olden days
So out of the above four options Indigo and Alizarin falls under the category of vat dye and hence the correct options for the given solution

Option A and B are the correct options.

Additional Information: Before the application of vat dyes they have to be solubilized (vetted) by adding sodium hydrosulphite and sodium hydroxide these are solubilized vat dye‐ sulphuric esters of leuco vat dyes When they are dissolved, they do not generally produce the same color as their parent vat dyes Like direct dyes they ionize in water they mostly have strong attraction for cotton and cellulosic fibers and they can be exhausted by the addition of sodium chloride.

Note: Vat dyes are insoluble in water and have to be dissolved in water by using sodium hydroxide and Sodium hydrogen sulphite usually at a temperature of ${50^ \circ }$ for almost a time period of $15 - 20\min$.