In a transformer the tappings are generally provided on

Answer: Option D

The correct answer is Option D: high voltage side.

Here's why:

When we put taps on the high voltage (HV) side of a transformer, it means that part of the winding has higher voltage but lower current for the same amount of power.
Because the current is lower on the HV side:
1. The wires needed for the tapping connections and the tap-changing switch (which moves between different tap points) can be thinner.
2. The switch itself (called a tap changer) can be much smaller, lighter, and less complex.
3. This makes the whole tap-changing mechanism significantly cheaper to build and maintain.

Now, let's look at why the other options are generally not preferred:
If taps were placed on the low voltage (LV) side (Option C), that side of the transformer carries a very high current.
1. Handling such high currents would require very thick wires for the tapping connections.
2. The tap-changing switch would need to be very robust, large, and heavy-duty to safely break and make connections carrying high current.
3. This would make the tap changer extremely expensive and bulky.

While Options A (primary side) and B (secondary side) can sometimes be the HV or LV side depending on whether the transformer is step-up or step-down, the general rule is to place taps where the current is lower to save cost and reduce complexity. This is almost always the high voltage side.
So, to keep the tap changer economical and practical, it's always placed on the side with lower current, which is the high voltage side.