Which of the following is the best reason as to why increasing the NaCl concentration increases the temperature at which the two strands of DNA "melt" apart?
A) Greater NaCl concentration correlates to greater ion concentration. DNA is a poly-anion and therefore exhibits a strong attraction for ions. NaCl forms chains of ionic interactions that bridge the two strands of the DNA and thus causing the melting temperature of the DNA strands to increase.
B) Greater NaCl concentration results in molecular precipitation. The higher the degree of molecular precipitation the higher the melting temperature of the two DNA strands.
C) Greater NaCl concentration results in stronger cross-strand hydrogen bonds. Stronger cross-strand hydrogen bonds results in an increase in the melting temperature of the two strands.
D) Greater NaCl concentration correlates to greater negative charge neutralization (shielding). Greater negative charge shielding reduces cross strand repulsion and thus increases the melting temperature of the two strands.