Right answer is (b) It is computed only when the element falls on the boundary of the domain on which tractions are known

For explanation I would say: In Finite Element Analysis, internal load vector Q is computed only when the element falls on the boundary of the domain on which tractions are specified (i.e., known). Computation of Q involves the evaluation of line integrals (for any type of element). In practice, it is convenient to express the surface traction t in the element coordinates. In that case, Q can be evaluated in the element coordinates and then transformed to the global coordinates using a transformation matrix.