The correct option is 1, 2, and 4 only because these processes contribute to the release of carbon dioxide (CO₂) into the atmosphere. Volcanic action releases CO₂ trapped in the Earth's crust, while respiration by living organisms converts organic materials into energy, releasing CO₂ as a byproduct. Additionally, the decay of organic matter involves decomposers breaking down dead organisms, which also releases carbon dioxide into the atmosphere. In contrast, photosynthesis uses carbon dioxide to produce oxygen and organic compounds, thus acting as a carbon sink rather than adding to atmospheric CO₂. This understanding is critical in comprehending human impact on climate change and carbon management within ecosystems, a key topic in environmental science for UPSC.