Answer:
Option A is correct
k = 2/5
Step-by-step explanation:
The rule of dilation with scale factor k is given by:

As per the statement:
Line AB has a length of 5 cm. The line segment is dilated to produce line A'B', which has a length of 2 cm.
⇒original Length (AB)= 5 cm
and
Image length (A'B') = 2 cm
Apply the rule of dilation we have;

Substitute the given values;

Therefore, the scale factor of the dilation is, 2/5