And question on airframe icing not mentioned in any books.
That is not true; there can hardly be a subject that is discussed in more detail: carburettor, pitot icing through to heavy airframe icing. Anti-icing and de-icing techniques and methods are also covered in detail.
Even i had to go Google for elt frequencies, not in study book, (been a while since atpl exams). Why ask such a question at ppl level?
Many ELTs in use are no longer fully receivable. It is important to know the correct ELT frequency (unit) that is monitored whatever the pilots qualification.
You don't mentioned the reading material used by your student. There are a lot of dodgy study material published by hopers and should not be used. Surely we instructors should ensure that our students follow the best and correct study material.