The correct answer is option (B):
If I were a king
The sentence "If I am a king I would give this order" uses the past subjunctive mood. This mood is used to express hypothetical or counterfactual situations, wishes, or unreal conditions. When the condition is contrary to fact, as in this case (the speaker is not a king), the past subjunctive is used in the 'if' clause. For the verb 'to be' in the past subjunctive with any subject (I, you, he, she, it, we, they), 'were' is used. Therefore, "If I were a king" is the grammatically correct construction.
Let's analyze the options:
'If I was a king' is incorrect because 'was' is the simple past tense and is generally not used in the past subjunctive for hypothetical situations. While some informal contexts might allow it, 'were' is the standard and universally accepted form for the past subjunctive.
'If I were a king' is correct as explained above, using the past subjunctive 'were'.
'If I being a king' is grammatically incorrect. 'Being' is a present participle and cannot function as the main verb in a conditional clause like this.
'If I are a king' is incorrect because 'are' is the present tense form of 'to be' for plural subjects or 'you'. It does not fit the hypothetical nature of the sentence.
Therefore, the correct replacement for the underlined part is "If I were a king".