What is rotational delay in input$/$output $(\frac{\frac{?}{?}}{O})$ scheduling?

It is the time required to move the read$/$write head from the current position to the desired data.

It is the time required to transfer the desired number of bits to or from the disk.

It is the time required to wait for the desired data item to pass under the read$/$write head.

It is the time required to wait for the desired track to pass under the read$/$write head.