When does the current drawn from a cell become maximum?

Eight identical cells,each having an electromotive force $E$ and internal resistance $r$,are connected in series to form a closed circuit. An ideal voltmeter is connected across $2$ cells. The voltmeter will read ........ $E$.

The variation of terminal potential difference $(V)$ with current $(I)$ flowing through a cell is as shown in the graph. The $EMF$ $(E)$ and internal resistance $(r)$ of the cell are:

Four identical cells of emf $E$ and internal resistance $r$ are to be connected in series. If one of the cells is connected wrongly,the equivalent emf and effective internal resistance of the combination are

Two identical cells,when connected either in parallel or in series,give the same current in an external resistance of $5\,\Omega$. The internal resistance of each cell will be $.............\,\Omega$.

$A$ galvanometer together with an unknown resistance in series is connected to two identical batteries each of $1.5\, V$. When the batteries are connected in series,the galvanometer records a current of $1\, A$,and when the batteries are in parallel,the current is $0.6\, A$. What is the internal resistance of the battery?