Answer:
b. is less than the launching speed.
Step-by-step explanation:
According to the law of energy conservation, the total mechanical energy remain the same. In our case the block starts with some kinetic energy, this energy is then lost to friction force, which dissipates as heat energy to external environment. Therefore, its kinetic energy when coming back must be less than its kinetic energy at launch, and the same for its speed, as mass is unchanged.