A long metallic bar is carrying heat from one of its ends to the other end under steady-state. The variation of temperature $\theta$ along the length $x$ of the bar from its hot end is best described by which of the following figures?

The ratio of the diameters of two metallic rods of the same material is $2 : 1$ and their lengths are in the ratio $1 : 4$ . If the temperature difference between their ends are equal, the rate of flow of heat in them will be in the ratio

Four identical rods of same material are joined end to end to form a square. If the temperature difference between the ends of a diagonal is ${100^o}C$, then the temperature difference between the ends of other diagonal will be ........ $^oC$

Two rods of same material have same length and area. The heat $\Delta Q$ flows through them for $12\,minutes$ when they are jointed in series. If now both the rods are joined in parallel, then the same amount of heat $\Delta Q$ will flow in ........ $\min$

Four rods of same material and having the same cross section and length have been joined, as shown. The temperature of junction of four rods will be........ $^oC$

Two identical square rods of metal are welded end to end as shown in figure $(a)$. Assume that $10\, cal$ of heat flows through the rods in $2\, min$. Now the rods are welded as shown in figure, $(b)$. The time it would take for $10$ cal to flow through the rods now, is ........ $\min$