The following is the arrangement of the given molecules in decreasing order of mass: 
<u>Solution:</u>
First inorder to arrange the elements in descending order of their mass we have to calculate the molecular mass of each element. The calculation is as follows:
<u>Mass of C6H14:</u>


<em>Mass of C6H14 is 86.172</em>
<u>Mass of NO2:</u>


<em>Mass of NO2 is 46.0055</em>
<u>Mass of Fe2O3:</u>


<em>Mass of Fe2O3 is 159.6882</em>
<u>Mass of CaCO:</u>


<em>Mass of CaCO will be 68.0874</em>
So, the order will be
which is 
Firework exploding. Thank you :)
Hello!
If there's an air bubble inside the buret, and the bubble escapes the buret during the titration the initial volume lecture (Vi) would be lower (closer to 0) than the actual one, and the recorded consumed volume (ΔV=Vf-Vi) would be higher than the actual one and thus the calculated concentration of the hydrochloric acid would be higher than the real one.
Have a nice day!
I believe it is D as you are hearing the copper tube