Correct Answer - Option 2 : 0.45 fck

**Explanation:**

The **permissible compressive stress in concrete is taken as 0.67 f**_{ck} and a partial factor of safety of 1.5 is applied to it. So, final stress comes out to be 0.45 f_{ck}.

- For design purposes, the
**compressive strength of concrete** is assumed to be 0.67 times the characteristic strength of concrete.
- The
**partial factor of safety of 1.5** is also to be applied in addition to this.
- Characteristic Strength of concrete Cube = fck
- Characteristic strength of concrete in actual structure = 0.67 fck
- Design strength of concrete in flexural compression =
**0.67 fck / partial FOS = 0.67fck / 1.5 = 0.45fck**