Which one of the following is the weakest kind of bonding in solids?

Which one of the following quantities does not have the unit of force per unit area?

$A$ $2 \,m$ long rod of radius $1 \,cm$ which is fixed from one end is given a twist of $0.8$ radians. The shear strain developed will be

The length of a rod under longitudinal tension $T_1$ is $L_1$ and that under longitudinal tension $T_2$ is $L_2$. What is the actual length of the rod,in the absence of tensions?

$A$ steel wire having a radius of $2.0 \, mm$, carrying a load of $4 \, kg$, is hanging from a ceiling. Given that $g = 3.1\pi \, m/s^2$, what will be the tensile stress that would be developed in the wire?

For the tangential stress on the cross-section $PQRS$ to be maximum,$\theta = $ ....... $^o$