First, you're going to be reporting on the database and you're going to want to get all details for students in a standard way - you won't want to do something like "plus Match and Science" to the query.
Second, the mandatory subjects could/will change. Most education authorities change their minds (or rather, the political masters change their minds). You may as well cater for this in your design so that when it happens, all you got to do is change your front end to the database (and you won't need to change the "plus Match and Science" stuff).
You're going to need a subject description in your Subject Master table but you've probably done enough to get a good grade.