This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Basics of DNA, Subject name: Biochemistry
At Tm or melting temperature, what percentage of dsDNA is denatured? 
Select and explain. 
A. 25%, B. 50%, C. 75%, D. 100%
B: 50%
Answer: B: 50% 
Explanation: Melting temperature or Tm Temperature when half (50%) of the helical structure is denatured. At lower temperature, the melted strands are re-associated; this is called annealing. When DNA is denatured, unstacking of bases occur resulting in increased absorbance at 260 nm-hyperchromicity