The correct option is A (b)
The option, with the error in it, is the correct option.
Option B: The error lies in "to find evidences" because 'evidence' is a mass noun and is usually written in its singular form.
The plural form 'evidences' is used in archaic texts, religious language or other specialized uses. The given sentence does not display any of these situations. Hence this part has an error.
So, option B is correct.
Option
A: There is no error in the part "The king was embarrassed"; it's in the past
tense and agrees to the rest of the sentence. Hence option A is
incorrect.
Option C: Similarly, the words "against his own queen"
also do not contain any error. Hence C is incorrect.
Option D is incorrect because the error lies in B.