Complete Question
The complete question is shown on the first uploaded image
Answer:
The concentration of
that should used originally is 
Explanation:
From the question we are told that
The necessary elementary step is

The time taken for sixth of 0.5 M of reactant to react 
The time available is 
The desired concentration to remain
Let Z be the reactant , Y be the first product and X the second product
Generally the elementary rate law is mathematically as

Where k is the rate constant ,
is the concentration of Z
From the elementary rate law we see that the reaction is second order (This because the concentration of the reactant is raised to power 2 )
For second order reaction

Where
is the initial concentration of Z which a value of 
From the question we are told that it take 9 hours for the concentration of the reactant to become


So


=> 
For 





Buoyancy is considered a physical property. It is a type of physical property because it is related to the density and weight of the item, which are both physical.
Answer:
The answer to your question is letter C. 3
Explanation:
Unbalanced chemical reaction
C₂H₄ + O₂ ⇒ CO₂ + H₂O
Reactants Elements Products
2 C 1
4 H 2
2 O 3
Balanced chemical reaction
C₂H₄ + 3O₂ ⇒ 2CO₂ + 2H₂O
Reactants Elements Products
2 C 2
4 H 4
2 O 6
The coefficient of Oxygen is three.