To solve this problem, we will use the principle of conservation of momentum.$\\$Given:$\\$• Mass of body A $= m \\$• Mass of body B $= m \\$• Initial velocity of body A $= v_1 \\$• Initial velocity of body B $= 0 \\$• Final velocity of both bodies after collision $= v_2 \\$Since the collision is completely inelastic, the two bodies stick together after the collision.$\\$Using the conservation of momentum:$\\$Initial momentum $=$Final momentum$\\ m \cdot v_1 + m \cdot 0 = (m + m) \cdot v_2 \\ m \cdot v_1 = 2m \cdot v_2 \\$Cancel $m$ from both sides:$\\ v_1 = 2v_2 \\$Thus, the ratio $v_1 : v_2$ is:$\\ v_1 : v_2 = 2 : 1 \\$Therefore, the correct option is 4.