The correct statement is option C: The block will come to rest when the work done by friction becomes equal to the change in energy stored in the spring.

Explanation:
When a block is attached to a spring and pulled away from its mean position, several forces come into play. These forces include the force applied to pull the block, the force of friction acting against the motion, and the force exerted by the spring.

1. Force applied to pull the block:
When the block is pulled away from its mean position, a force is applied to overcome the resistance offered by the spring. This force is responsible for stretching or compressing the spring.

2. Force of friction:
The force of friction opposes the motion of the block. As the block moves, the friction force acts in the opposite direction of its motion. The friction force is responsible for dissipating the energy and eventually bringing the block to rest.

3. Force exerted by the spring:
The spring exerts a force on the block that is proportional to the displacement from its mean position. This force tries to restore the block to its equilibrium position.

Now, let's consider the different scenarios:

- If the block crosses the mean position (option A), it means that the force applied to pull the block is greater than the force exerted by the spring. In this case, the block will continue to move until the forces are balanced or the block reaches another equilibrium position.

- If the block comes to rest when the forces acting on it are exactly balanced (option B), it means that the force applied to pull the block is equal to the force exerted by the spring. In this scenario, the block will stop moving, but it may not necessarily be at the mean position.

- The correct statement (option C) is that the block will come to rest when the work done by friction becomes equal to the change in energy stored in the spring. This means that the friction force gradually dissipates the energy provided by the force applied to pull the block. As the energy stored in the spring decreases, the force exerted by the spring also decreases until it becomes balanced with the friction force. At this point, the block will come to rest at the mean position.

In summary, option C is the correct statement because it considers the balance between the work done by friction and the change in energy stored in the spring, leading to the block coming to rest at the mean position.