The question is incomplete, here is the complete question:
At elevated temperature, nitrogen dioxide decomposes to nitrogen oxide and oxygen gas

The reaction is second order for
with a rate constant of
at 300°C. If the initial [NO₂] is 0.260 M, it will take ________ s for the concentration to drop to 0.150 M
a) 1.01 b) 5.19 c) 0.299 d) 0.0880 e) 3.34
<u>Answer:</u> The time taken is 5.19 seconds
<u>Explanation:</u>
The integrated rate law equation for second order reaction follows:
![k=\frac{1}{t}\left (\frac{1}{[A]}-\frac{1}{[A]_o}\right)](https://tex.z-dn.net/?f=k%3D%5Cfrac%7B1%7D%7Bt%7D%5Cleft%20%28%5Cfrac%7B1%7D%7B%5BA%5D%7D-%5Cfrac%7B1%7D%7B%5BA%5D_o%7D%5Cright%29)
where,
k = rate constant = 
t = time taken = ?
[A] = concentration of substance after time 't' = 0.150 M
= Initial concentration = 0.260 M
Putting values in above equation, we get:

Hence, the time taken is 5.19 seconds
Answer:
Lithium has 5 elements, sulphur has 2 elements and oxygen has 4 elements
The significant figures will be 1.
As, weight of acetylsalicylic acid = 0. 4 g
We obtain 400 mg when we convert 0.4g of acetylsalicylic acid to mg.
So, 400 milligrams are worth 0.4 grams when converted to grams.
There is just one significant figure because 0 before a decimal is not significant i.e. 4.
<h3><u>What are significant figures?</u></h3>
The digits of a number that have relevance in relation to the measurement's resolution are known as significant figures. Additionally known as significant figures in chemistry. All experimental measurements are subject to some degree of uncertainity.
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