A block of mass M is attached to the lower end : of a vertical spring. The spring is hung from a ceiling and has force constant value k. The mass is released from rest with the spring initially unstretched. The maximum extension produced in the length of the spring will be :

Question

( A ) $Mg/k$
( B ) $2Mg/k$
( C ) $4Mg/k$
( D ) $Mg/2k$