Strictly speaking, you are not liable as you area full time student. If you google 'council tax discounts' there are loads of links regarding discounts and liability for council tax.
However, to keep the peace and harmony it may just be easier to pay your share (if you can afford it), there is nothing laid down to say you have to pay but it may be part of your tenancy agreement, in which case you will probably have to pay.
Maybe phone the local council or Citizens Advice Bureau for advice.