List of top Questions asked in CBSE Class X

The gap between two neurons is called a
Explain the following terms with one example each. 
(a) Corrosion 
(b) Rancidity
Oil and fat containing food items are flushed with nitrogen. Why?
Which of the following is a plant hormone?
Why do we apply paint on iron articles?
A shiny brown coloured element ‘X’ on heating in air becomes black in colour. Name the element ‘X’ and the black coloured compound formed.
Explain the following in terms of gain or loss of oxygen with two examples each. 
(a) Oxidation
(b) Reduction
What do you mean by a precipitation reaction? Explain by giving examples.
State two ways to prevent the rusting of iron.
In the electrolytic refining of a metal M, what would you take as the anode, the cathode and the electrolyte?
Name two metals which will displace hydrogen from dilute acids, and two metals which will not.
What are amphoteric oxides? Give two examples of amphoteric oxides.
In the refining of silver, the recovery of silver from silver nitrate solution involved displacement by copper metal. Write down the reaction involved.
You are given a hammer, a battery, a bulb, wires and a switch.
  1. How could you use them to distinguish between samples of metals and non-metals?
  2. Assess the usefulness of these tests in distinguishing between metals and non-metals.
Food cans are coated with tin and not with zinc because
What is the difference between displacement and double displacement reactions? Write equations for these reactions.
Write one equation each for decomposition reactions where energy is supplied in the form of heat, light or electricity.
An element reacts with oxygen to give a compound with a high melting point. This compound is also soluble in water. The element is likely to be
Why are decomposition reactions called the opposite of combination reactions? Write equations for these reactions.
Which of the following methods is suitable for preventing an iron frying pan from rusting?
Why is respiration considered an exothermic reaction? Explain.
What does one mean by exothermic and endothermic reactions? Give examples.
Write the balanced chemical equation for the following and identify the type of reaction in each case. 
(a) Potassium bromide(aq) + Barium iodide(aq) \(→\) Potassium iodide(aq) + Barium bromide(s) 
(b) Zinc carbonate(s) \(→\) Zinc oxide(s) + Carbon dioxide(g) 
(c) Hydrogen(g) + Chlorine(g) \(→\) Hydrogen chloride(g) 
(d) Magnesium(s) + Hydrochloric acid(aq) \(→\) Magnesium chloride(aq) + Hydrogen(g)
A doctor has prescribed a corrective lens of power +1.5 D. Find the focal length of the lens. Is the prescribed lens diverging or converging?
Find the focal length of a lens of power −2.0 D. What type of lens is this?