You must have seen tarnished copper vessels being cleaned with lemon or tamarind juice. Explain why these sour substances are effective in cleaning the vessels.

Why do curd and sour substances not be kept in copper vessels ?

Why should curd and sour substances not be kept in brass and copper vessels?

Take things which are sour in taste and used as food. Eg. Curd, lemon juice. If you check these substances with blue and red litmus what happens ?

Very often you must have seen traffic police catching motorists and scooter drivers who drive fast and fine them. Does fine for speeding depend on average speed or instantaneous speed ? Explain.

Sudheer wants to make his vessels, which are made of Brass and copper, clean and shiny. What suggestions you would like to give him?

Assertion (A) : Pickles and sour substances are not stored in brass and copper vessels. Reason: Acids reacts with metals. A) 'A' and 'R' are correct. R is a correct reason for A. B) 'A' and 'R' are correct. R is not a correct reason for A. C) 'A' is correct, but 'R' is wrong. D) 'A' is wrong, but 'R' is correct.

You may have seen in a circus a motorcyclist driving in vertical loops inside a ‘death- well’ (a hollow spherical chamber with holes, so the spectators can watch from outside). Explain clearly why the motorcyclist does not drop down when he is at the uppermost point, with no support from below. What is the minimum speed required at the uppermost position to perform a vertical loop if the radius of the chamber is 25 m ?

Take vinegar, lemon juice, soapy water, baking soda in different vessels. Pur beetroot pieces in the vessels. Predict what happens. Verify your prediction by observing the changes. After 10 minutes, 30 minutes, 60 minutes record your observations. What do you conclude?