One ends of a conducting rod is maintained at temperature ${50}^0\mathrm{C} \mathrm{and} \mathrm{at} \mathrm{the} \mathrm{other} \mathrm{end} \mathrm{ice} \mathrm{is} \mathrm{melting} \mathrm{at} 0^0\mathrm{C}.$ The rate of melting ice is doubled if

the temperature is made ${200}^0\mathrm{C}$ and the area of cross-section of the rod is doubled

the temperature is made ${100}^0\mathrm{C}$ and area of cross section of rod and length both are doubled.

the temperature is made ${100}^0\mathrm{C}$ and length of the rod is made four times

area of cross section of the rod is halved and length is doubled.