A

Step 1: Understand the scenario: The block of ice and the lead shot are floating on water at 0ºC.
Step 2: Recognize that ice melting does not change the water level because of Archimedes' principle: the weight of water displaced is equal to the weight of the ice. However, the lead shot, being heavier than water, affects the situation.
Step 3: The lead shot, which is denser than water, will sink and displace additional water as the ice melts completely.
Step 4: Consequently, once the lead shot settles at the bottom, there is an increase in the water level due to the additional displacement caused by the lead shot that is now submerged.
Therefore, the overall water level in the vessel rises when the ice melts completely.