Aradioactive isotope has a half-life of ten days. how much of a 100 gram sample will be left after 20 days

25

Explanation:

after10 days it would be 50 then it would be 25 after another 10

the answer is to check all of them! they all apply well at least i think so!

answer: 802.3 kilo joules of energy represents 191.75 kilo calorie of energy.

explanation:

energy released during combustion of one mole methane = 802.3 kilo joules

if 1 kilo joule = 0.239006   kilo calorie

then ,802.3 kilo joule will be = 802.30.239006 kilo calorie

802.3 kilo joule = 191.75 kilo calorie

hence, the energy in kilo calorie is 191.75 kilo calorie.