Answer:
option B.
Step-by-step explanation:
given,
Mass of the blocks 1 = M
Mass of the blocks 1 = 2 M.
initial speed of the block 1= v
initial speed of the block 2 = - v
where V is the final speed of the blocks after collision
using conservation of momentum
M v + 2 M (-v) = (M + 2 M) V
3 M V = - M v
velocity of the blocks after collision is equal to -v/3 m/s
hence, the correct answer is option B.