In using an HSI to fly LOC(BC) approach, the arrow should be set to which direction?

When using a Horizontal Situation Indicator (HSI) to fly a Localizer Back Course (LOC(BC)) approach, the correct direction for the arrow is the front course bearing, which is the reciprocal of the localizer's final approach course. This means that when you are approaching from the back of the localizer, the arrow will indicate the correct heading to fly to intercept the localizer signal.

On a HSI, the indication you are looking for enables you to remain aligned with the approach path accurately. Setting the arrow to the front course bearing ensures that during the approach, you are effectively flying towards the localizer signal, allowing you to make the necessary adjustments to maintain that alignment.

The other options do not provide accurate guidance for this type of approach. The reciprocal of the desired course may be relevant in other contexts, but for the LOC(BC) approach, what you need is specifically the front course bearing to ensure proper navigation and alignment with the approach path.