What substance is present in a solution consisting solely of electrolytes?

Electrolytes are substances which are capable of producing a solution that has the ability to conduct electricity. These electrolytes are formed from the dissociation of salts into ions. The positive ions are named cations while the negative ions are termed anions. 

Hence, the answer to these item is SALT. Salt are substances produced by the reaction of cations and anions. 

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.