Write an application to your headmaster / headmistress requesting him / her to arrange few extra classes to carry out the Practical of Chemistry.

 Dear [Headmaster/Headmistress],

I hope this letter finds you well. I would like your assistance in arranging a few extra classes for the practical sessions of our Chemistry course.

As you know, Chemistry is a subject that requires hands-on experience and practical application in order to fully grasp its concepts. Our current class schedule does not provide enough time for us to conduct the necessary experiments and laboratory work, which is crucial for our understanding of the subject.

Given this situation, I kindly request that a few extra classes be arranged, so that we can have enough time to carry out the practical sessions and complete the course effectively. I believe this will greatly benefit the students and help us achieve better results.

Thank you for your time and consideration. I look forward to hearing back from you soon.

Sincerely,

[Your Name]