What is the tangential stress on the cross-section $PQRS$?

Two blocks of masses $1 \,kg$ and $2 \,kg$ are connected by a metal wire going over a smooth pulley. The breaking stress of metal is $\frac{40}{3 \pi} \times 10^6 \,N m^{-2}$. What should be the minimum radius of the wire used if it should not break (in $mm$)? $(g = 10 \,m s^{-2})$

Match the following:

Column-$I$	Column-$II$
$(A)$ Shear modulus	$(I)$ Resistance to change in volume
$(B)$ Shearing stress	$(II)$ Proportionality constant
$(C)$ Elastic fatigue	$(III)$ Tangential stress
$(D)$ Modulus of elasticity	$(IV)$ Temporary loss of elastic property
	$(V)$ Resistance to change against deformation force

The correct match is:

Statement $(A)$ For an ideal liquid,the bulk modulus is infinite and the shear modulus is zero.
Statement $(B)$ The volume contraction of a metal cube of bulk modulus $140 \text{ GPa}$ and side length $10 \text{ cm}$,when subjected to a hydraulic pressure of $7 \times 10^6 \text{ Pa}$,is $-0.05 \text{ m}^3$.
Statement $(C)$ $A$ spiral spring is stretched by a weight attached to it. The strain is tensile.

$Dyne/cm^2$ is not a unit of

$A$ metal wire is clamped between two vertical walls. At $20 ^o C$,the unstrained length of the wire is exactly equal to the separation between the walls. If the temperature of the wire is decreased,the graph between elastic energy density $(u)$ and temperature $(T)$ of the wire is: