Which one of the following is used during 'RNA i' process, to silence the desired gene ?

The correct option is dsRNA (double-stranded RNA).

RNA interference (RNAi) is a biological process in which RNA molecules inhibit gene expression or translation, neutralizing targeted mRNA molecules. During this process, double-stranded RNA ($\mathrm{dsRNA}$) is introduced or produced inside the cell.
This $\mathrm{dsRNA}$ is recognized and cleaved by the enzyme Dicer into short double-stranded fragments called small interfering RNAs (siRNAs). These fragments are then incorporated into the RNA-induced silencing complex (RISC), where the strands are separated, allowing the guide strand to bind to the complementary target messenger RNA (mRNA) and facilitate its degradation, thereby silencing the desired gene.