https://sciencing.com/make-3d-model-atom-5887341.html
An index fossil is a fossil that is useful for dating and correlating the strata in which it is found.
Or it is a fossil that helps you find the date where it has been found. I rephrased that.
Answer: D) It conducts electricity when it is dissolved in water
Answer : The half life of 28-Mg in hours is, 6.94
Explanation :
First we have to calculate the rate constant.
Expression for rate law for first order kinetics is given by:

where,
k = rate constant
t = time passed by the sample = 48.0 hr
a = initial amount of the reactant disintegrate = 53500
a - x = amount left after decay process disintegrate = 53500 - 10980 = 42520
Now put all the given values in above equation, we get


Now we have to calculate the half-life.



Therefore, the half life of 28-Mg in hours is, 6.94
Answer : The total mass of oxygen gas released in the reaction will be, 12.8 grams
Explanation :
Law of conservation of mass : It states that mass can neither be created nor be destroyed but it can only be transformed from one form to another form.
This also means that total mass on the reactant side must be equal to the total mass on the product side.
The balanced chemical reaction will be,

According to the law of conservation of mass,
Total mass of reactant side = Total mass of product side
Total mass of
= Total mass of 
or,
Total mass of
= Mass of
+ Mass of 
As we are given :
Total mass of
= 16.12 grams
The mass of
= 9.72 grams
So,
Total mass of
= Mass of
+ Mass of 


Therefore, the total mass of oxygen gas released in the reaction will be, 12.8 grams