Following the passing of Queen Elizabeth II, Charles III was formally declared the new monarch of Britain, continuing the British royal lineage.
Step 1: Understanding the succession
The eldest son of Queen Elizabeth II, Charles ascended the throne as per the rules of hereditary monarchy.
Step 2: Analysis of options
- Charles III is the correct title taken by the new monarch.
- Other options such as George IX, Charles VI, and Edward VII are previous monarchs or incorrect titles.
Therefore, option (A) is the correct answer.