Why does the coefficient of performance of a refrigerator become infinity?

$A$ refrigerator is to maintain eatables kept inside at $9^{\circ} C$. If room temperature is $36^{\circ} C$,calculate the coefficient of performance.

Why can the coefficient of performance of a refrigerator never be infinite?

The power of a refrigerator that can make $15 \ kg$ of ice at $0^{\circ}C$ from water at $30^{\circ}C$ in one hour is: (in $W$)

In a refrigerator,one removes heat from a lower temperature and deposits it to the surroundings at a higher temperature. In this process,mechanical work has to be done,which is provided by an electric motor. If the motor is of $1\,kW$ power and heat is transferred from $-3\,^{\circ}C$ to $27\,^{\circ}C$,find the heat taken out of the refrigerator per second,assuming its efficiency is $50\%$ of a perfect engine.

Explain the working of refrigerators/heat pumps and their coefficient of performance.