Bond and anchorage — for M 150 mix concrete as per Indian practice, the recommended local bond stress (unit bond stress) is closest to:

Introduction / Context:Local bond stress (also referred to as unit bond stress) is used for checks related to bar anchorage, development length, and bond splitting in working-stress-era calculations. Recognizing typical tabulated bond stresses for common concrete grades remains a frequent exam topic and aids quick preliminary sizing.

Given Data / Assumptions:

• Concrete grade: M 150 (nominal mix context).
• Plain understanding of bond stress values for educational problems.
• Bars are assumed to be under standard bond conditions (not poor or special).

Concept / Approach:

Permissible local bond stresses historically increase with concrete grade because stronger concrete provides better rib interlock and higher bond capacity. For M 150, the widely cited value for local bond stress in traditional references is approximately 10 kg/cm² for average conditions.

Step-by-Step Solution:

Verification / Alternative check (if short method exists):

For detailed work, development length Ld = (ϕ * σ_s) / (4 * τ_bd) can be checked using the tabulated τ_bd for M 150 and the working steel stress; the result aligns with using ≈10 kg/cm² here.

Why Other Options Are Wrong:

5 kg/cm² is too low; 15–25 kg/cm² exceed typical M 150 bond values for average conditions.

Common Pitfalls (misconceptions, mistakes):

Confusing local bond with average bond; mixing values for higher concrete grades; forgetting modifications for deformed bars or poor bond conditions.

Final Answer:

10 kg/cm²