Which DNA molecule among the following will melt at lowest temperature ?

Which of the following DNA will melt at the lowest temperature?

Which of the following will DNA melt at the lowest temperature?

Which of the following melts at a certain temperature ?

Among the following which has lowest pK_a value?

Melting temperature for double stranded DNA is the temperature at which 50% of the double stranded molecules are converted into single stranded molecules. Which one of the following DNA will have the highest melting temperature ?

Which among the following has higher melting point