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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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Observe the following picture a write down the chemical reaction with the explanation.
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Write scientific reason.
Elements belonging to the same group have the same valency.
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Write scientific reasons.
Lemon or tamarind is used for cleaning copper vessels turned greenish.
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Complete the process of iron rusting by filling the blanks. Suggest a way to prohibit the process.
The iron rust is formed due to........................... reaction. Different
regions on iron surface become anode and cathode.
Reaction on anode region :
`F_e(s) → Fe^(2+) (aq) +2e^-`
Reaction on anode region :
`O_2(g) + 4H^+(aq) +............................ → 2H_2 O (l) `
When Fe2+ ions migrate from anode region they react with ................... to form Fe3+ ions.
A reddish coloured hydrated oxide is formed from ............... ions. It is called rust.
`2Fe_(3+) (aq) + 4H_2O(l) → ................. + 6H_+(aq) `
A way to prevent rusting ..................................................................
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Identify the process shown in the diagram and explain it in short
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Answer the following question.
a) What is meant by corrosion?
b) Write names of any two methods of prevention of corrosion.
c) In which method, metal like copper, aluminium are coated with a thin layer of their oxides by means of electrolysis.
d) Explain this method with diagram.
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