In this reaction 50% of the compound decompose in 10.5 min thus, it is half life of the reaction and denoted by symbol 
.
(a) For first order reaction, rate constant and half life time are related to each other as follows:
Thus, rate constant of the reaction is 
.
(b) Rate equation for first order reaction is as follows:
![k=\frac{2.303}{t_{1/2}}log\frac{[A_{0}]}{[A_{t}]}](https://tex.z-dn.net/?f=k%3D%5Cfrac%7B2.303%7D%7Bt_%7B1%2F2%7D%7Dlog%5Cfrac%7B%5BA_%7B0%7D%5D%7D%7B%5BA_%7Bt%7D%5D%7D)
now, 75% of the compound is decomposed, if initial concentration ![[A_{0} ]](https://tex.z-dn.net/?f=%5BA_%7B0%7D%20%5D)
is 100 then concentration at time t ![[A_{t} ]](https://tex.z-dn.net/?f=%5BA_%7Bt%7D%20%5D)
will be 100-75=25.
Putting the values,
On rearranging,
Thus, time required for 75% decomposition is 21 min.
The identity of the substance is Iron.
<h3>Properties of Iron</h3><h3>Chemical properties</h3>
- The element iron has the atomic number 26 and the symbol Fe
- Electronic configuration of Fe is [AR] 3d6 4s2
- The atomic weight of Iron is 55.847
- The element iron belong to the group VIII of the periodic table
- It is the fourth most prevalent element in the crust of the world
- It is a highly reactive element as it gets rusted readily in the moisture of air
<h3>Physical properties</h3>
- It is a heavy metal in the first transition series
- The color of iron is silvery grey
- High malleability and ductility
- It has a strong electrical conductivity.
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It's the rows. They are periods. (1,2,3,4,5,6,7 - the ones without the letters).
Its A because I did it on connexus
