If mean annual soil temperature is 8–15°C and seasonal difference < 5°C, the regime is

Correct option is B

The correct answer is (B) Isomesic

Explanation:
• Soil temperature regimes are used in soil classification (Soil Taxonomy) based on the Mean Annual Soil Temperature (MAST).
• The prefix "Iso-" is added to the temperature regime name when the difference between the mean summer and mean winter soil temperatures is less than $5°C$ (at a depth of $50 cm$).
• Mesic regime applies to soils with a MAST between $8°C$ and $15°C$.
• Therefore, a soil with a MAST of $8-15°C$ and a seasonal variation of less than $5°C$ is classified as Isomesic.

Information Booster:
• Other common temperature regimes include:
• Cryic: $< 8°C$ (cold).
• Thermic: $15°C$ to $22°C$.
• Hyperthermic: $> 22°C$.
• In India, mostly Hyperthermic and Thermic regimes are found.

Additional Knowledge:
• Mesic (Option A): MAST is $8-15°C$ but the seasonal difference is greater than or equal to $5°C$.
• Thermic (Option C): MAST is $15-22°C$ with a seasonal difference $\ge 5°C$.
• Isothermic (Option D): MAST is $15-22°C$ with a seasonal difference $< 5°C$. This is often found in tropical highlands.