at all temperatures

at one particular temperature

when system is under thermal equi-librium

at critical temperature

direct mixing of hot and cold fluids

a complete separation between hot and cold fluids

flow of hot and cold fluids alternately over a surface

generation of heat again and again

is black in colour

reflects all heat

transmits all heat radiations

abslprbs heat radiations of all wave lengths falling on it

black bodies

polished bodies

all coloured bodies

all of the above

3

6

9

81