Raj holding a $10 \mathrm{Kg}$ iron bar says to Neelam who is holding a bag of $10 \mathrm{Kg}$ cotton that his iron bar is heavier. Neelam refused. Whose article was heavier ?

Neelam's bag containing $10 \mathrm{Kg}$ cotton is heavier than Raj's iron bar.
As we Know 
$\mathrm{True} \mathrm{weight} =\mathrm{Apparent} \mathrm{weight}+\mathrm{Upthrust}$
Now, the bag of cotton will have more volume due to its low density than iron bar. Hence, cotton bag will experience more upthrust due to air and will be heavier.