After 62.0 hours , 1.0 g remains unchanged from a sample of 42k . how much 42k was in the original sample?

The half-life of K-42 is 12.360 hours.

62 hours is just about 5 half-lives, so we'd expect about 1/32 of the original amount to remain after that time. (32 = 2^5)

In fact, it's 12.36 / 62 = 5.016 half-lives.

2^5.016 = 32.36

So if you started with 32.36g in the original sample, it would have decayed down to 1g after 5.016 half-lives.

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 to this is the 3rd choice!