Yes, you can definitely write the GATE exam in any stream (including Data Science and Artificial Intelligence) even if your BTech is in Chemical Engineering.

GATE doesn't restrict you to appearing in an exam related to your BTech specialization. You can choose any of the GATE subject areas offered, which includes Computer Science and Information Technology (CSIT) for Data Science and Artificial Intelligence.

While your Chemical Engineering background might not directly translate to Data Science and AI, you can prepare for the GATE CSIT exam with focused self-study or coaching. Numerous resources like textbooks, online courses, and practice questions are available to help you build the necessary knowledge and skills.

Familiarize yourself with the GATE CSIT syllabus, which covers topics like Algorithms, Data Structures, Programming Languages (like Python), Database Management Systems, Machine Learning, and Artificial Intelligence.

While a good GATE score is crucial, some MTech programs in Data Science and AI at IITs and NITs might have additional requirements. These could include a minimum percentage in your BTech or a statement of purpose (SOP) highlighting your interest and motivation for the field.

Data Science and AI are popular fields, and competition for MTech seats in IITs and NITs can be high. A strong GATE score and a well-prepared SOP (if required) will be essential for securing admission.

Overall, with dedication and the right preparation, you can crack the GATE CSIT exam and pursue an MTech in Data Science and Artificial Intelligence at IITs or NITs, even with your BTech in Chemical Engineering.

I hope it helps!