Development (embedment) length — for M 150 concrete with average bond conditions (average bending stress 6 kg/cm²), the required embedment length for a bar of diameter d as per IS 456 is approximately:

Introduction / Context:
Development length (also called embedment length) ensures that reinforcing bars can safely transfer stress to the surrounding concrete without bond failure. In working-stress/older tabulated approaches used alongside M 150 concrete (nominal 1:2:4), the development length is often quoted as a multiple of the bar diameter d under average bond conditions. This question assesses recognition of that typical multiple for design memory work.

Given Data / Assumptions:

• Concrete grade: M 150 (nominal mix context).
• Average bond conditions and average bending stress 6 kg/cm² stated.
• Bar in tension; diameter = d (goal is Ld expressed as a multiple of d).

Concept / Approach:

General bond design uses the relationship Ld = (phi * sigma_s) / (4 * tau_bd), where phi is bar diameter, sigma_s is steel stress to be developed, and tau_bd is design bond stress (dependent on concrete grade and bar type). For M 150 concrete and typical working-stress levels historically used in many references, the tabulated or memory value corresponding to average conditions is approximately 58 d for tension development in plain/deformed reinforcement at the indicated stress level.

Step-by-Step Solution:

Verification / Alternative check (if short method exists):

A more rigorous derivation would require tau_bd from tables and sigma_s from permissible stress for the steel grade, but for this exam-style prompt, the remembered multiple suffices.

Why Other Options Are Wrong:

28 d, 38 d, and 48 d are insufficient for the specified stress level with M 150; 95 d is unnecessarily high for the stated conditions.

Common Pitfalls (misconceptions, mistakes):

Using development lengths from higher concrete grades; forgetting that tension development length is longer than for compression; overlooking modifications for deformed bars and hooks where applicable.

Final Answer:

58 d