A hot plane surface at 100°C is exposed to air at 25°C with a combined heat transfer coefficient of 20W/m2*K The heat loss from the surface is to be reduced by half by covering it with sufficient insulation with a thermal conductivity of 0.1 W/m*K. Assuming the heat transfer coefficient to remain constant, the required thickness of insulation is

(a) 0.1cm
(b) 0.5 cm
(c) 1.0 cm
(d) 2.0 cm
(e) 5 cm