The expected answers are:

(a)Tensile stress - is the force acting on a unit cross sectional area (of a wire/rod)

OR

Force per unit cross sectional area (of a wire/rod)
(b)Tensile strain is the extension per unit length i.e. extension
                                                                                             length .
(c)Yield point is the minimum stress/load, acting on an elastic material, beyond which plastic deformation sets in.
OR
Yield point is a point on a load/stress, versus extension/strain graph that represents the least force/stress beyond which plastic deformation sets in.

This question was on definition of terms related to the elastic properties of matter. It was quite popular among the candidates. The candidates also performed fairly well. A good number of the candidates were able to correctly define tensile stress and tensile strain. However, most of the candidates could not define yield point correctly.