A hallow enclosure is formed between two infinitely concentric cylinders of radii 1m and 2m respectively. Radiative heat exchange takes place between the inner surface of the larger cylinder (surface-2) and the outer surface of the smaller cylinder (surface-1) the radiating surfaces are diffuse and the medium in the enclosure is non – participating. The fraction of the thermal radiation leaving the larger surface and striking itself is
(a) 0.25 (b) 0.5 (c) 0.75 (d) 1