**Buoyant Force and Sinking of a Metal Block in Water**

When a metal block is thrown into a deep lake, it will sink in the water due to its higher density compared to water. As the block sinks deeper in the water, the buoyant force acting on it remains the same.

**Explanation:**

1. **Buoyant Force:** The buoyant force is the upward force exerted by a fluid (in this case, water) on an object immersed in it. It is equal to the weight of the fluid displaced by the object.

2. **Density of the Metal Block:** The metal block has a higher density than water, which means it is heavier per unit volume. This is why it sinks in water.

3. **Sinking in Water:** The metal block sinks in water due to the force of gravity pulling it downward. As it sinks deeper, the water exerts an upward buoyant force to counteract the weight of the block.

4. **Weight and Buoyant Force:** The weight of the metal block remains constant as it sinks deeper because the force of gravity acting on it does not change. However, the buoyant force also remains constant because it depends on the weight of the fluid displaced by the block, which does not change as the block sinks.

5. **Balanced Forces:** When an object is in equilibrium (no net force acting on it), the weight of the object is balanced by the buoyant force. In the case of the sinking metal block, the weight of the block is balanced by the constant buoyant force acting on it.

6. **No Change in Buoyant Force:** Since the buoyant force remains constant, the answer to the question is option 'B' - the buoyant force remains the same as the metal block sinks deeper in the water.

**Summary:**

In summary, when a metal block is thrown into a deep lake, it sinks in the water due to its higher density. As it sinks deeper, the buoyant force acting on it remains the same. The buoyant force is equal to the weight of the fluid displaced by the object, and since the weight of the block and the volume of water displaced remain constant, the buoyant force does not change.