The half-life of radon-216 is 5 days. If a sample contains 20 grams, how much was present 20 days ago? *

the answers would be

the first one and the second one

your answer is a. the enthalpy of formation for a pure element in its standard state is always positive.

for step 7 table c on the lab "newtons law of action"   the average time it took the car to travel .25 meters   was 1.92 seconds.

the average time it took the car to travel 0.50 meters was 2.61 seconds

hope this : )