Answer
$(C)\ 290\frac{N}{m}$
Work Step by Step
We can find the force constant as
$F=\frac{K}{x}$
$\implies K=\frac{F}{x}$.......eq(1)
Now $slope=x=\frac{1.7mm-0}{0.5N-0}=3.4\frac{mm}{N}$
We plug in the known values in eq(1) to obtain:
$K=\frac{1.0}{3.4mm\times \frac{1m}{1000mm}}=290\frac{N}{m}$
