$n$ equal resistors are first connected in series and then connected in parallel. What is the ratio of the maximum to the minimum resistance?

In an aluminium $(Al)$ bar of square cross-section,a square hole is drilled and is filled with iron $(Fe)$ as shown in the figure. The electrical resistivities of $Al$ and $Fe$ are $2.7 \times 10^{-8} \ \Omega m$ and $1.0 \times 10^{-7} \ \Omega m$,respectively. The electrical resistance between the two faces $P$ and $Q$ of the composite bar is

What is the equivalent resistance between $A$ and $B$?

$A$ uniform conductor of resistance $R$ is cut into $20$ equal pieces. Half of them are joined in series and the remaining half of them are connected in parallel. If the two combinations are joined in series,the effective resistance of all the pieces is

$A$ $3 \ V$ battery with negligible internal resistance is connected as shown in the figure. The current $I$ in the circuit will be ............ $A$.

By which of the following single load resistance should the load bridge be replaced so that the power to the load remains unchanged (in $Omega$)? (Given $r = 3 \ \Omega$ for each resistor in the bridge)