Which of the following statements is incorrect?

$A$ body of mass $10 \, kg$ is attached to the end of a wire of length $0.3 \, m$. If the breaking stress of the wire is $4.8 \times 10^7 \, N/m^2$ and its cross-sectional area is $10^{-6} \, m^2$,what is the maximum angular velocity in $rad/sec$ with which it can be rotated in a horizontal plane without breaking the wire?

$A$ spring is stretched by applying a load to its free end. The strain produced in the spring is

Which of the following materials is non-crystalline?

If the breaking stress of a wire is $3.18 \times 10^{10} \, N/m^2$,what should be its minimum radius so that the wire does not break? (Refer to the figure for the masses attached to the pulley system,assume $g = 10 \, m/s^2$)

If the breaking force for a given wire is $F$, then the breaking force of two wires of the same material and same dimensions joined together in parallel will be