Accede

The word "accede" can be used in two contexts, the first being one where it means to agree to a demand or a request and the second instance where it means to assume office or position.
In option A, the word correctly used as the manager can accede to a request. 
In option B, again the usage is correct as it can be difficult to accede to a proposal. 
In option D, the usage is appropriate as assuming the throne can be rephrased as acceding to the throne.
But in option C, the usage is incorrect as here the word "demands" means requirements or needs and the correct usage would be "meet" or "fulfil".
So the correct choice is C.