Step-by-step explanation:
It is given that,
Let m is the mass of the object that is hung from a vertical spring of unknown spring constant k. When the spring is stretched by 17 cm, the object executes SHM. Let T is the period of oscillation that is given by :
.............(1)
The gravitational force is balanced by the force of spring at equilibrium as :

So, equation (1) becomes :

x = 17 cm = 0.17 m

T = 0.82 seconds
So, the period of this oscillation is 0.82 seconds. Hence, this is the required solution.