Question

Rewrite the following sentences correctly:
The box of chocolates are very expensive.

Answer 1

The box of chocolates are very expensive.

The sentence could be written as "The box of chocolates is very expensive" and "The box of chocolates are most expensive."  

Answer 2

The sentence could be properly written as 
The box of chocolates IS very expensive 

We are not using are here because we are talking about the "box" which is only one so therfore,  we'll use is not are.