What is the shape of the graph of stress $\to$ strain up to the elastic limit?

Which of the following is the correct pair?

If the length of a wire is doubled,what is the strain?

Two wires as shown in the figure below, made of steel, have a breaking stress of $12 \times 10^8 \text{ N/m}^2$. The area of cross-section of the upper wire is $0.008 \text{ cm}^2$ and that of the lower wire is $0.004 \text{ cm}^2$. The maximum mass that can be added to the pan without breaking any wire is . . . . . . kg. (Take $g = 10 \text{ m/s}^2$)

Two blocks of masses $3 \, kg$ and $5 \, kg$ are connected by a metal wire going over a smooth pulley. The breaking stress of the metal is $\frac{24}{\pi} \times 10^{2} \, Nm^{-2}$. What is the minimum radius of the wire? (Take $g = 10 \, ms^{-2}$) (in $cm$)

$A$ rod is placed on a smooth horizontal surface. What is the stress developed when the temperature is increased by $40\,^{\circ}C$?
$[\alpha = 5\, \times\, 10^{-5}\,^{\circ}C^{-1},\, Y = 5\, \times\, 10^{11}\, N/m^2]$