B
The answer should be B.....
Chemical energy is the kind of energy stored in the bonds formed by atoms and molecules in chemical compounds and elements. This energy is released during a chemical reaction and heat is often given out in the process. These kind of reactions where heat is given out as a by product are called exothermic reactions.
The major factor that determines how much chemical energy a substance has is the mass of that substance. Mass is defined as the amount of matter in a substance.
The higher the mass of a substance, the more concentrated that substance is and subsequently the greater the number of atoms and molecules.
Logically, the higher the number of atoms and molecules then the greater the number of bonds in that substance and subsequently the more the amount of chemical energy stored therein.
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
According to the law of conservation of mass, the mass of reactants will be equal to the mass of the products. The mass of products and reactants will only differ during a nuckear reaction
Changing of the physical state of water is not a nuclear reaction. So becoz of that the mass will remain constant without any change.