Step 1: Concept Gasification is the conversion of solid biomass into a combustible gas mixture known as producer gas or syngas.
Step 2: Meaning This conversion occurs at very high temperatures ($700 - 1000^{\circ}$C) with a limited supply of oxygen or steam.
Step 3: Analysis Because the process relies on high heat (thermal) to trigger chemical reactions that break down biomass molecules, it is classified as a thermo chemical conversion process.
Step 4: Conclusion Gasification is thermo chemical in nature.
Final Answer: (A)