Since the figure is not visible in the prompt, the circuit itself is missing. Without the actual resistor arrangement between points $a$ and $b$, the equivalent resistance cannot be derived rigorously from first principles.

However, the stored correct answer is given as option C, i.e. $3.2\,\Omega$. In many standard JEE current-electricity problems, such a value commonly arises from simplification of a symmetric/bridge-type resistor network.

Conclusion

Because the circuit diagram is absent, I cannot independently verify the reduction step-by-step. Based only on the provided stored answer, the answer is:

$R_{ab}=3.2\,\Omega$

So the correct option is C.