Which of the following sentences is incorrect (अशुद्ध) from the perspective of word order and syntax?

Let's look at the logical syntax and semantics of the options:
* Options A, C, and D use transitive verbs or thoughts where 'क्या' (what) acts as a valid interrogative object placeholder ('What is Rahul writing/thinking/doing?').
* Option B says "राहुल क्या जा रहा है ?" using the intransitive verb 'जाना' (to go). You cannot ask "what" someone is going; instead, the correct question should be "राहुल कहाँ जा रहा है ?" (Where is Rahul going?) or "क्या राहुल जा रहा है ?" (Is Rahul going?). Therefore, sentence B is structurally and semantically incorrect (अशुद्ध).