Correct Answer : Option (C) :   Both magnetically and electrically coupled.

Explanation : Auto-transformers is a transformer with one common winding for primary and secondary, wound on a common core.

If you have a winding with a minimum of one tapping, you have an autotransformer. One extreme terminal in common for input and output. Two terminals are used for input, usually supply voltage, while the third terminal gives output with a common terminal. It is even possible to have more than one output.

In Auto Transformer, one single winding is used for primary winding and secondary winding, which means the primary and secondary windings have the common single winding. Therefore, the primary is electrically connected to the secondary and magnetically coupled to it.

Such an autotransformer saves on the cost of copper, and losses are less; flux linkage is better since there is just one winding. It is also smaller in size compared with a normal transformer.