Final answer:
The most appropriate restoration after a pulpotomy in an extensively decayed second primary molar is a stainless steel crown due to its durability and full-coverage protection.
Step-by-step explanation:
After a pulpotomy in a second primary molar with extensive occlusal caries, the most appropriate restoration is a stainless steel crown. Resin-modified glass ionomer, bonded amalgam, and composite resin do not provide the necessary durability or full coverage that is required for a primary tooth with extensive decay. Given that the goal of a restoration is to be non-destructive and reversible while preventing further decay or infection, a stainless steel crown is ideal because it encompasses the entire tooth, ensuring protection against future caries, and maintains the integrity of the molar until it's time for the tooth to naturally exfoliate.