The heat conduction per unit time is given by,

dq/dt = k(t - t)A/l

=> dq/dt = k(t - t)πr²/l

=> dq/dt ∝ r²/l

hence we can see that the heat conduction is directly proportional to the radius and inversely proportional to the length.

So heat conduction is maximum when r is maximum and l is minimum.

Hence the rod with maximum radius and minimum length will conduct maximum heat.

This is an important chapter too as 1 question is usually asked always especially in NEET or cet.  So prepare well and keep practicing more and more mcqs to build your concepts strong.

Best wishes.

Thank you.