An object weighs $10 \, N$ in air. When immersed fully in water,it weighs only $8 \, N$. The weight of the liquid displaced by the object will be (in $, N$)

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 milkman in our society started carrying a lactometer. His move was well appreciated by the society members.
$(a)$ What is the use of a lactometer? On what principle does it work?
$(b)$ What values of the milkman are shown by this move?

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?

$(a)$ Name the two factors on which the buoyant force depends.
$(b)$ State the relationship between the buoyant force on an object and the weight of the liquid displaced by it.

Kanchan purchased gold from a jeweller. She was,however,very apprehensive about the purity of the gold purchased by her. Ultimately,she approached a person who claimed he could test its purity by making certain measurements of weight of the gold in air and water.
$(a)$ What principle was he making use of for testing purity?
$(b)$ Write the relation by which he found the relevant quantity.
$(c)$ What value did Kanchan imbibe?