The planet Earth itself is considered to be a closed system because there is a limit to the amount of matter that is exchanged. However, there are open systems that are ON Earth.
Answer:
Muscular contractions that moves food along the digestive tract.
2.258625 *10²³ oxygen atoms will be produced.
<h3><u>Explanation:</u></h3>
Decomposition reaction is defined as the type of reaction where one single reactant breaks to produce more than one product only by means of heat or other external factor.
Formula of magnesium oxide = MgO.
The molecular mass of magnesium oxide = 24 +16= 40.
So in 40 grams of magnesium oxide, number of molecules is 6.023 * 10²³.
So in 15 grams of magnesium oxide,, number of molecules is 6.023 *1023 * 15/40 = 2.258625 *10²³.
From one molecule of magnesium oxide, one oxide atom will be produced.
So number of oxide atoms with 100% yeild = 2.258625 *10²³
Answer: It will take 29 years for a 10.0-gram sample of strontium-90 to decay to 5.00 grams
Explanation:
Radioactive decay process is a type of process in which a less stable nuclei decomposes to a stable nuclei by releasing some radiations or particles like alpha, beta particles or gamma-radiations. The radioactive decay follows first order kinetics.
Half life is the amount of time taken by a radioactive material to decay to half of its original value.
Half life is represented by 

= rate constant
Given : Strontium-90 decreases in mass by one-half every 29 years , that is half life of Strontium-90 is 29 years.
As half life is independent of initial concentration, it will take 29 years for a 10.0-gram sample of strontium-90 to decay to 5.00 grams as the amount gets half.