Series aiding means that the magnetic fields produced by the two coils are in the same direction and add up to produce a stronger magnetic field. In the case of overlapping flux lines of two energized coils, the flux lines will be in the same direction and therefore the coils are said to be in series aiding.

Explanation:
When two coils are energized with an electric current, they produce a magnetic field around them. The magnetic field consists of flux lines that indicate the direction and strength of the magnetic field. When the flux lines of two coils overlap, it means that the magnetic fields produced by the coils interact with each other.

In the case of series aiding, the flux lines of the two coils are in the same direction. This means that the magnetic fields produced by the coils add up to produce a stronger magnetic field. This can be visualized by imagining two arrows representing the direction of the flux lines. When the arrows are pointing in the same direction, they add up to form a longer arrow, indicating a stronger magnetic field.

Series aiding is beneficial in many applications. For example, in transformers, it allows for efficient energy transfer from one coil to another. When the flux lines of the primary coil and the secondary coil overlap in a transformer, they are in series aiding, which helps in the transfer of electrical energy from the primary coil to the secondary coil.

In contrast, series opposing would mean that the flux lines of the two coils are in opposite directions. This would result in a cancellation of the magnetic fields, leading to a weaker overall magnetic field.

Therefore, in the case of overlapping flux lines of two energized coils, the correct answer is option 'A' - series aiding.