Question

A molecule of DNA (deoxyribonucleic acid)
lies along a straight line. It is 1.472

Answer 1

I'm going to assume that 'singly ionized' means each end aquires or loses a single electron, giving a charge at each end of +/- 1.6*10^-19 C
The force between the two ends is given by Coulomb's law:
F=KqQ/r^2
where q and Q are the charges, K is the coulomb constant and r is the distance between them.

We also know that for
F=Sx
where S is the spring constant of the spring and x is the extension of the spring, which in this case is 1.5% of the distance between them, r. So we can write
x=- 0.015r
It is negative because the spring is compressed, rather than extended. Substitute this into F=Sx, to find:
F=-S*0.015*r

And force which causes the spring to be compressed is the force due to the charges, so we can write:

-0.015Sr=KqQ/r^2
rearrange to make S the subject:
k=-KqQ/0.015r^3

K=8.99*10^9
q=1.6*10^-19
Q=-1.6*10^-19
r=3.404*10^-6

S= -(8.99*10^9)(1.6*10^-19)(-1.6*10^-19) / (3.404*10^-6)^3
S=5.83*10^-12 N/m