Question

An allotrope of carbon which is as tensile as steel is?

Answer 1

Carbon nanotube, also called buckytube, nanoscale hollow tubes composed of carbon atoms. The cylindrical carbon molecules feature high aspect ratio length to diameter values typically above ${10^3}$ with diameters from about $1$ nanometer up to tens of nanometers and lengths up to millimeters.

Complete answer:
Carbon nanotubes, is the allotrope of carbon which is as tensile as steel. Carbon nanotubes are tubes made of carbon with diameters typically measured in nanometers. The shortest carbon nanotube is the organic compound cycloparaphenylene, having eight phenyl rings connected through para positions.
Carbon nanotubes can exhibit remarkable electrical conductivity, while others are semiconductors. They also have exceptional tensile strength and thermal conductivity because of their nanostructure and strength of the bonds between carbon atoms. In addition, they can be chemically modified. Carbon nanotubes aspect ratio. Carbon nanotubes are very elastic elongation to failure. They have very high tensile strength.
We have found that the work function of the nanotubes is $0.1 - 0.2eV$ larger than that of highly oriented pyrolytic graphite of which the valence state is $\sigma - \pi$ orthogonal. This result is ascribable to reflection of the $\sigma - \pi$ mixed valence state in the case of carbon nanotubes.

Note:
Carbon nanotubes can act as antennas for radios and other electromagnetic devices. Conductive carbon nanotubes are used in brushes for commercial electric motors. They replace traditional carbon black. The nanotubes improve electrical and thermal conductivity because they stretch through the plastic matrix of the brush.