What mass of copper is equivalent to 0.7 mole (Cn=63.5)

 The buffer solution with best  buffering capacity is the 0.882 M HF and 0.418 M

Explanation:

A buffer solution works best when having equal amount of both molecules. The buffer capacity will last until the last mol of the conjugate acid (HF) or the conjugate base (F) is consumed, and then, the pH will change significantly.

The best option is the 0.882 M HF and 0.418 M, because both molecules have higher concentrations than other options, that means,  this Buffer solution will last longer because it has more moles to be consumed when adding an acid or a base.