The half life of an element X is 5 days. If we have 10g of X intially, what is the mass of X for 5 days

Answer 1

I assume you mean what is the mass of X AFTER 5 days/
The half life is 5 days so 1/2 the mass will disappear in 5 day. So 1/2 of 10 = 5. It is important for you to realize that it's the mass of element X that will go away but that the "sample" may not decrease by 1/2.

Answer 2

Please give full details

Answer 3

What's to explain? Half life of element X is 5 days. It has a mass of 10 grams initially. In a 5 day period the resulting amount of the element X will now be 5 grams. Then I added a caveat. If you have element X of 10 grams with a half life of 5 days, at the end of 5 days you will have 5 grams of element X but you will had 5 grams of element X left PLUS the decay products of element X which might weigh 5 grams or a little more the 5 grams or a little less than 5 grams depending upon what the decay products are. What you see is that half of the radioactive element X disappeared but you still have half of it left plus whatever the decay products are.