What would happen if we place denatured DNA in acidic medium?

Hello and welcome Nandini Yadav,

It is worth mentioning DNA is an acid (Deoxyribonucleic acid) and intracellular pH is most commonly between 7.0 and 7.4.

Alkaline reagent Example

"The sodium hydroxide (NaOH) is a commonly used reagent to denature the DNA by increasing the pH. At an alkaline pH, OH- groups are predominant. They remove the hydrogen- bonds-contributing protons from guanine and thymine, thus breaking the hydrogen bonds between the two oligonucleotides."

Source

You can see in the image below hydrogen bonds between nucleotides Adenine (A), Cytosine (C), Guanine (G) and Thymine (T).

Acid reagent Example

A decrease in the pH was found to deteriorate the thermal stability of DNA

Source

At an acidic pH, the H+ in the surrounding environment of DNA is high and therefore the hydrogen bonds between Adenine (A) and Thymine (T), Cytosine (C) - Guanine (G) will 'break'.

More information here.