The water in lake fair has a salinity of 12 ppt. the water
a. is saltier than the ocean
b. has 12 grams of salt per 1000 grams of water
c. has a greater salinity than ocean water
d. doesn't contain any dissolved salts

it mean that the water : B. has 12 grams of salt per 1000 grams of water SAlinity measures the amount of salt compard to the amount of water. 1 ppt means that there is 1 grams of salt per 1000 grams of water. so, 12 ppt means 12 grams of salt per 1000 grams of water

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. 

Ido not understand.