The correct option is
C Isn't he
The correct answer is Option B.In the given question we are to choose the correct question tag that completes the sentence.
A question tag is a grammatical structure in which a declarative statement or an imperative is turned into the interrogative. For e.g., in the sentence "You are John, aren't you?", the statement "You're John" is turned into a question tag "aren't you". It is used to confirm the statement or encourage a reply.
There are certain rules to be followed while forming question tags.
A positive statement is followed by a negative question tag and vice versa.
In the given sentence 'Amitabh Bachchan is' is the statement that has to be turned into the interrogative. This statement is a positive one and thus the question tag will be negative. Therefore, 'is' will become 'isn't he'. We use the pronoun he because the doer is a male. Hence Option B is the correct answer.
Option A is incorrect since it is a question tag in the positive and as discussed above a positive statement becomes negative when turned into a question tag.
Options C and D are question tags in the past tense. A question tag always follows the tense of the statement. The statement in the given question is in the present tense and hence the question tag should also be in the present tense and not the past tense.
Hence Options A, C, and D are not the correct options and Option B is the correct answer.