ANS:D -

The lever arm (x) of a singly reinforced beam is the distance from the centroid of the compressive force block to the centroid of the tensile force block. It's a crucial parameter in determining the bending moment and the distribution of stresses in the beam. The lever arm (x) can be calculated using the formula: 3x=d−3n​ Where:

• d is the effective depth of the beam.
• n is the depth of the neutral axis.

This formula is derived from the assumption of a rectangular stress distribution in the concrete compression zone and a linear stress distribution in the tensile steel reinforcement. The lever arm represents the moment arm about which the bending moment acts, and it determines the magnitude of the bending stresses induced in the beam. So, to calculate the lever arm of the beam, you would use the formula 3x=d−3n​.