Which substance chars when heated with conc. $ {H_2}S{O_4} $ ?
A. Carbohydrates
B. Hydrocarbon
C. Fat
D. Protein

Hint: Carbohydrates are defined as optically active polyhydroxy aldehydes or polyhydroxy ketones or compounds which give such compounds on hydrolysis. Carbohydrates are a class of naturally occurring organic compounds of carbon, hydrogen and oxygen which are primarily produced by plants, these are formed in plants by a process known as photosynthesis and make about $ 70 % $ of the solid plant material.

Complete answer:
Sulphuric acid is the strong dehydrating agent and one of the most important industrial chemicals worldwide.
When conc. $ {H_2}S{O_4} $ Comes in contact with sugar, it becomes black due to dehydration. The sulphuric acid dehydrates the sugar (carbohydrate), removes the hydrogen and oxygen atoms releasing water as a product and carbon is left behind.
 $ {C_{12}}{H_{22}}{O_{11}}\xrightarrow{{conc.{H_2}S{O_4}}}12C + 11{H_2}O $
The charring reaction of carbohydrate with concentrated sulphuric acid is one of the confirmation of the dehydrating power of $ {H_2}S{O_4} $ .
Now coming to other options -The Gerber method is the chemical test to determine the fat content of substances, Milk fat is separated from protein by adding sulphuric acid. Sulphated oil is obtained by reacting animal or vegetable oils with sulphuric acid or $ S{O_3} $ gas. The sulfation is the process of treating oil with concentrated sulfuric acid to get oil that can be emulsified in water.
Concentrated sulfuric acid is used to remove unsaturated hydrocarbon impurities from saturated aliphatic hydrocarbons.
Carbohydrates chars when heated with concentrated $ {H_2}S{O_4} $ .
Therefore the correct answer is option A.

Note:
Proteins are high molecular mass complex biomolecules of amino acids present in all living cells. All proteins on partial hydrolysis give peptides of varying molecular masses which on complete hydrolysis gives $ \alpha - $ amino acid. Thus, chemically proteins are condensation polymers in which the monomer units are $ \alpha - $ amino acids.