The maximum magnitude of shear stress due to shear force F on a rectangular section of area A at the neutral axis, is

τmax is the maximum shear stress. In mechanics, shear stress is defined as the component of stress coplanar with a material cross-section. It's a measure of the internal forces acting on a material in response to an applied load. In the case of a rectangular section subjected to a shear force, the maximum shear stress occurs at the neutral axis, which is the line of zero stress running through the center of the section perpendicular to the applied shear force. The magnitude of the maximum shear stress is given by the formula τmax = F/2A, where F is the applied shear force and A is the area of the cross-section. so the ans should be B

Shear stress = VQ/Ib
here, V=F
Q=Ay
=b*d/2*d/4 [d=depth, b=width of cross section of beam ]
I=bd^3/12
so, Shear stress= 3F/2A

Maximum Share stress * Avg. share stress = 1.5
1.5 * F/A = 15F/10A = 3F/2A