If jd is the lever arm and $$\sum {\text{O}} $$ is the total perimeter of reinforcement of an R.C.C. beam, the bond stress at the section having Q shear force, is A. $$\frac{{\text{Q}}}{{2{\text{jd}}\sum {\text{O}} }}$$ B. $$\frac{{\text{Q}}}{{3{\text{jd}}\sum {\text{O}} }}$$ C. $$\frac{{\text{Q}}}{{{\text{jd}}\sum {\text{O}} }}$$ D. $$2\frac{{\text{Q}}}{{{\text{jd}}\sum {\text{O}} }}$$

The correct answer is $\boxed{\frac{{\text{Q}}}{{{\text{jd}}\sum {\text{O}} }}}$.

The bond stress is the force per unit area that resists the tendency of the reinforcement to pull out of the concrete. It is calculated by dividing the shear force by the area of the reinforcement and the lever arm. The lever arm is the distance from the neutral axis to the centroid of the reinforcement. The total perimeter of reinforcement is the sum of the perimeters of all the reinforcing bars in the beam.

The bond stress is an important factor in the design of reinforced concrete beams. It must be sufficient to prevent the reinforcement from pulling out of the concrete, but it should not be so high that it causes cracking in the concrete.

The other options are incorrect because they do not take into account the lever arm.