In the figure provided the blocks B and C have mass m each. The strings AB and BC are light, having tension T1 and T2 respectively. The system is in equilibrium with a constant horizontal force mg acting on C. It can be assumed that the dimensions of the block are negligible.
The tension in the lower string T2 can be divided into vertical and horizontal components. The horizontal component is `T2*cos theta_2` and this is equal to m*g. The vertical component is `T2*sin theta_2` = m*g
`(T2*sin theta_2)/(T2*cos theta_2) = (mg)/(mg) = 1`
=> `tan theta_2 = 1`
The option B is true.