List of top Science Questions asked in CBSE Class X

Give reasons why copper is used to make hot water tanks and not steel (an alloy of iron).
A man went door to door posing as a goldsmith. He promised to bring back the glitter of old and dull gold ornaments. An unsuspecting lady gave a set of gold bangles to him which he dipped in a particular solution. The bangles sparkled like new but their weight was reduced drastically. The lady was upset but after a futile argument the man beat a hasty retreat. Can you play the detective to find out the nature of the solution he had used?
What is the function of receptors in our body? Think of situations where receptors do not work properly. What problems are likely to arise?
The brain is responsible for
The gap between two neurons is called a
Which of the following is a plant hormone?
A shiny brown coloured element ‘X’ on heating in air becomes black in colour. Name the element ‘X’ and the black coloured compound formed.
What do you mean by a precipitation reaction? Explain by giving examples.
Name two metals which will displace hydrogen from dilute acids, and two metals which will not.
In the electrolytic refining of a metal M, what would you take as the anode, the cathode and the electrolyte?
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.
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?
What is meant by power of accommodation of the eye?
Translate the following statements into chemical equations and then balance them. 
(a) Hydrogen gas combines with nitrogen to form ammonia. 
(b) Hydrogen sulphide gas burns in air to give water and Sulphur dioxide.
(c) Barium chloride reacts with aluminium sulphate to give aluminium chloride and a precipitate of barium sulphate. 
(d) Potassium metal reacts with water to give potassium hydroxide and hydrogen gas.