The current relating to corresponding situations are as follows:
(i) Without any external resistance in the circuit
$I_1 = E/r$
The current in this case would be maximum, so I1= 4.2A
(ii) With resistance R1only
$I_2 = E/(r + R_1)$
The current in this case will be the second smallest value, so I2= 1.05 A
(iii) With R1and R2in series combination
$I_3 = E/(r+ (R_1+R_2))$
The current in this case will be minimum as the resistance will be maximum, so I = 0.42 A.
(iv) With R1and R2in parallel combination-
$I_4 = E/(r +((R_1R_2)/(R_1 +R_1)))$
The current in this case would be the second largest value, so I = 1.4 A.