Correct answer only !

four 3 ω resistors placed in series would provide a resistance that is equivalent to one ω resistor.

Option D

Explanation:

Resistors are said to be connected in “Series”, when they are daisy chained together in a single line. Since all the current flowing through the first resistor has no other way to go it must also pass through the second resistor and the third and so on. Then, resistors in series have a Common Current flowing through them as the current that flows through one resistor must also flow through the others as it can only take one path.

Total Resistance = R₁ + R₂ +R₃ +R₄ ohm

Note then that the total or equivalent resistance, R has the same effect on the circuit as the original combination of resistors as it is the algebraic sum of the individual resistances.

Total resistance R = 3 + 3 + 3 +3

                             = 12 ohm