according to the statement given what is the magnitude of the velocity of the rock just before it strikes the ground

Answer 1

I have no idea what the statement is but in general if you drop something with no initial speed
v = sqrt (2 g h)
where h is height in meters
g = 9.81 m/s^2 on earth
v is in meters/second

If you used copy and paste, it does not work here and I can not see your problem.