Which bond connects two consecutive nucleotides to form a dinucleotide?

What are the structures called that give an appearance as 'beads-on-string' in the chromosomes when viewed under an electron microscope?

If the length of $DNA$ in an organism is $2.72 \,mm$,how many base pairs will be present in this organism?

In a $DNA$ molecule,if the base ratio $(A+T)/(G+C)$ is $0.3$ and the amount of $A+T$ nitrogenous bases is $30,000$,what will be the amount of $G+C$ nitrogenous bases in the $DNA$ (in $,000$)?

What is the approximate molar concentration of $DNA$ in a human cell?

In the structure of a nucleotide, the phosphate group is attached to which carbon of the sugar (in $5'$)?