Final answer:
King Charles faced significant political unrest and religious tensions (option A) upon becoming king, including issues with religious sects, Parliament relations, fiscal chaos, and concerns about succession.
Step-by-step explanation:
What King Charles faced when becoming king can best be described as political unrest and religious tensions. After Charles's coronation in 1660, he encountered several critical issues. These included how he would handle the plethora of religious sects that had emerged during the 1650s, the future relationship between the monarchy and Parliament, especially regarding financial support, and succession concerns given that Charles had no children and his likely heir, his brother James, was a Catholic in a primarily Anglican realm.
Charles I's inability to work constructively with Parliament led to his decision not to call Parliaments, resulting in fiscal chaos and weakening England's position in European affairs. Additionally, his reign was marked by the rebellion and persecution of the nonconformists, signaling a nation deeply divided.