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Electrolysis is used to obtain pure metal from impure metal.
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Write scientific reason.
Farsightedness, this defect can be corrected by using convex lens.
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Explain the factors affecting the rate of chemical reaction with example.
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Explain the following reaction with their balanced chemical equation.
Hydrogen sulphide reacts with sulphur dioxide.
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Explain the following reaction with the balanced equation.
Aluminium reacts with dil hydrochloric acid
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Explain the following reaction with the balanced equation.
Reaction of zinc with dil hydrochloric acid
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Write a short note on the galvanometer.
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Find the power of a convex lens of focal length of + 25 cm.
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If focal length of a convex lens is 20 cm at what is the power of the lens?
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Balance the given chemical reaction as per the instructions below.
\[\ce{NaOH + H2SO4 -> Na2SO4 + H2O}\]
Oxidation means losing electrons then what is reduction?
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Identify the type of chemical reaction given below:
\[\ce{2Mg + O2 -> 2MgO}\]
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When hydrogen gas is passed over black copper oxide, a reddish-coloured layer of copper is formed.
Answer the questions that follow based on this reaction.
- Write the equation.
- What type of reaction is it?
- Complete the blanks:
In this reaction, an oxygen atom goes away from CuO (copper oxide), which means that ______ of copper oxide takes place, whereas a hydrogen molecule takes up an oxygen atom and water (H2O) is formed, meaning ______ of hydrogen takes place.
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Answer the questions based on the equation below:
\[\ce{CH3 - CH2 - OH ->[{[O]}][K2Cr2O7/H2SO4] CH3 - COOH}\]
- What type of reaction is it?
- What is the role of the chemical written on the arrow?
- Give one example of one such type of chemical as in answer (b).
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It is recommended to use air tight containers for storing oil for a long time.
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The power of convex lens of focal length 20 cm is ______.
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Identify the figure and give its use.

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Suggest measures in bursting fire crackers in festivals and processions.
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Explain the role of citizen in pollution control.
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Compare roasting and calcination.
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