From the given sentence, form a feminine noun from the masculine word given:
The Duke of Wales inaugurated the function.
 

In general English usage, the female kind of the noun ‘Duke’ is ‘Duchess’. A duke is remarked as a human who holds the best title in Britain. Unlike a prince, becoming a duke doesn't require an individual to be of royal blood and may be bestowed upon someone by the king or queen on the throne of england. However, sometimes it's an inherited position. the feminine person occupying an analogous position is understood as duchess. Hence, option c is that the correct option.
The empress is mentioned as a woman who holds the best sovereign power or rank in an empire. She is at a better position than a duchess. The masculine kind of ‘empress’ is ‘emperor’. Therefore, option a is an incorrect option. Similarly, a queen is mentioned as a sovereign of an independent state, usually under an empire. She comes below the empress, although the terms’ queen’ and ‘empress’ are often used interchangeably. The masculine sort of ‘queen’ is ‘king’. Therefore, option b is additionally not an accurate option.