Cells in Series and in Parallel

A battery consists of a variable number ($n$) of identical cells, each having an internal resistance $r$ connected in series. The terminal of the battery is short-circuited. A graph of current versus the number of cells will be as shown in figure.

Assertion: When cells are connected in series to the external load the effective e.m.f. increases.

Reason: The cells help each other in sending the current to the external load.

Two cells, having the same emf are connected in series through an external resistance $R$ . Cells have internal resistances $r_1$ and $r_2\mathrm{ }\left(r_1>r_2\right)$ respectively. When the circuit is closed, the potential difference across the first cell is zero. The value of $R$ is -

Which of the following are true, when the cells are connected in series?