Three $V-I$ graphs are drawn individually for two resistors and their series combination. Out of $A, B, C$,which one represents the graph for the series combination of the other two? Give a reason for your answer.

(C) We know that for a $V-I$ graph,the slope represents the resistance $(R = V/I)$.
In a series combination,the equivalent resistance $(R_s = R_1 + R_2)$ is always greater than the individual resistances ($R_1$ and $R_2$).
Therefore,the graph with the highest slope represents the series combination.
In the given graph,line $C$ has the maximum slope compared to lines $A$ and $B$.
Thus,$C$ represents the series combination of the other two resistors.