If the dissolution of borax in water is spontaneous, is the change in enthalpy positive or negative - or are both signs possible?

"Both signs are possible" is the correct choice.

Explanation:

The indication including its change in enthalpy depends on the concentration.As when the enthalpy seems to be negative besides purposeful unexpected temperatures lower, as well as successful for necessary response at extremely high temperatures.  

As such that when both signals could have been the enthalpy change.

Mass is the amount of matter in an object.  weight is the measurement of the pull of gravity on an object.  say for example, you travel to the moon which has a different gravitational field compared to the gravitational field of earth. (gravitational fields: earth = 1, moon = 0.165)  now when you are on the moon, the pull of gravity on you is different than on the earth. and as weight is the measurement of the pull of gravity on an object, that means yes, your weight can and will change on the moon.  however, on the moon, on earth or even on jupiter, the amount of mass inside of you remains the same. meaning your physical mass remains constant.  in conclusion it is possible for your weight to change as your mass remains constant. 

The answer is probably c. xylem