The mass of the wing affects the likelihood of flutter. A lighter wing is more susceptible to a high frequency flutter. For aerodynamic and stability purposes, the fuel may, therefore, be retained in the wing tanks, both inner and outer, not only to reduce the stress on the wing spar, but also to reduce the onset of flutter and increase lateral stability.

Regarding this question, it's worth noting that all the options are given in kilograms. Additionally, the question provides a fuel density of 0.8, which means we can't directly utilize the "kg" data from the provided figure. Instead, we need to calculate the total usable fuel in liters and then apply the fuel density (x 0.8). Assuming the pilot decides to refuel only the wing tanks, both inner and outer, for the aforementioned purposes, the total available fuel on-board will be:

• [(Outer tanks x 2) + (Inner tanks x 2)] x 0.8 = [(880 ltr x 2) + (6924 ltr x 2)] x 0.8 = 12 486 kg