just wondering, when the home office receive your apps, do they charge you full fee immediately even though they may reject your application? 

thanks.

As far as I know,
the home office will charge you for the full fee once the process of reviewing your documents starts.
If, in the unlucky case, your application is rejected, the Home office should return part of the fee payed by you. The amount is related to the expenses for the citizenship cerimony, but I have no elements to quantify it.

I hope this helps

Good luck