What do you mean by buoyancy?

You have a bag of cotton and an iron bar,each indicating a mass of $100\, kg$ when measured on a weighing machine. In reality,one is heavier than the other. Can you say which one is heavier and why?

An object is placed one by one in three liquids having different densities. The object floats with $\frac{1}{9}$, $\frac{2}{11}$, and $\frac{3}{7}$ parts of its volume outside the liquid surface in liquids of densities $d_1$, $d_2$, and $d_3$ respectively. Which of the following statements is correct?

On a voyage in their yacht,John and his father came across an iceberg. John advised his father to keep away from the iceberg. His father said that it is just a small piece of ice jutting out of the sea and there is nothing to bother. John told his father that icebergs are dangerous and narrated the story of the ship $Titanic$,which was sunk by an iceberg. John explained to his father why the iceberg was dangerous. This convinced his father,and they steered clear of the iceberg.
$(a)$ Why are icebergs in the sea dangerous?
$(b)$ What values are possessed by John and his father?

Gautam visited a fair along with his classmates. There he found that a hawker was selling balloons filled with helium gas. His teacher told the students that the balloons will rise in the sky and then stop after some distance. Gautam questioned his teacher as to why the balloons would stop. He started arguing with his teacher that the balloons would rise indefinitely. His teacher got irritated with him. Just then,Gautam's friend Avdesh took him aside and explained to him that the teacher was correct. The explanation given by Avdesh satisfied Gautam.
$(a)$ Why will the balloon stop after rising to a certain height?
$(b)$ What values are shown by Avdesh and Gautam?

The volume of a $500\, g$ sealed packet is $350\, cm^3$. Will the packet float or sink in water if the density of water is $1\, g\, cm^{-3}$? What will be the mass of the water displaced by this packet?