List of top Science Questions asked in CBSE Class X

In the following experimental setup of electrolysis of water, if P and Q are the gases collected in the test tubes enclosing the electrodes R and S, then select the option/options in which the matching is correct: 
(i) P - Oxygen gas, R - Anode 
(ii) P - Hydrogen gas, S - Cathode 
(iii) Q - Hydrogen gas, R - Cathode 
(iv) Q - Oxygen gas, S - Anode 

A student placed a candle flame at different distances from a convex lens and focused its image on a screen. He recorded his observation in tabular form as given below:
A student placed a candle flame at different distances from a convex lens and focused its image
The growth movements of plant parts in which the direction of the stimulus determines the direction of the response is known as tropic movements or tropism. Plants also have non-directional movements which may not be growth dependent.
growth movements of plant parts
Study the circuit shown in which two resistors X and Y of resistances 3 Ω and 6 Ω respectively are joined in series, with a battery of 2 V
two resistors X and Y of resistances 3 Ω and 6 Ω
Many pure metals like copper, iron and gold are very soft and as such are considered unsuitable for certain uses. Metallic objects around us such as cooking utensils, statues, ornaments, guns etc. are actually not made up of pure metals. Instead of pure metals, alloys are used in the design of most of the useful objects. Making alloys enhances the basic properties of a metal which is the primary constituent (metal) of an alloy.
What is stainless steel? How is it prepared? Write one important property which makes it more useful in making cooking utensils as compared to its primary metal.
Give two methods used to grow rose and jasmine plants by vegetative propagation.
Give one example each of a unisexual flower and a bisexual flower. Mention the changes which a flower undergoes after fertilization.
Many pure metals like copper, iron and gold are very soft and as such are considered unsuitable for certain uses. Metallic objects around us such as cooking utensils, statues, ornaments, guns etc. are actually not made up of pure metals. Instead of pure metals, alloys are used in the design of most of the useful objects. Making alloys enhances the basic properties of a metal which is the primary constituent (metal) of an alloy.
What are alloys? How is 'Brass' (an alloy) prepared?
What are soaps? Write the structure of a soap molecule. Explain the cleansing action of a soap. Why are soaps not considered suitable for washing clothes in a region where water is hard? How is this problem overcome?
Many pure metals like copper, iron and gold are very soft and as such are considered unsuitable for certain uses. Metallic objects around us such as cooking utensils, statues, ornaments, guns etc. are actually not made up of pure metals. Instead of pure metals, alloys are used in the design of most of the useful objects. Making alloys enhances the basic properties of a metal which is the primary constituent (metal) of an alloy.
Name an alloy used for welding two wires together in an electric circuit. Write its major constituents.
Name an alcohol and a carboxylic acid having two carbon atoms in their structures. Draw their structures and state how this alcohol can be converted into a carboxylic acid. What happens when these two compounds react in the presence of an acid? Write chemical equations for the reactions involved in the two cases mentioned above.
Many pure metals like copper, iron and gold are very soft and as such are considered unsuitable for certain uses. Metallic objects around us such as cooking utensils, statues, ornaments, guns etc. are actually not made up of pure metals. Instead of pure metals, alloys are used in the design of most of the useful objects. Making alloys enhances the basic properties of a metal which is the primary constituent (metal) of an alloy.
How does electrical conductivity and melting point of a metal change when it is converted to its alloy by mixing a small amount of an element in it?
Write one function each of the parts - (i) petals (ii) anther (iii) style and (iv) ovary of a bisexual flower.
List two causes of this defect.
Name the method by which Amoeba and Leishmania reproduce. Write a major difference in the way they divide to produce new individuals.
Determine the focal length of the lenses used in the spectacles.
What are magnetic field lines? How is the direction of magnetic field at a point determined? Draw the pattern of magnetic field lines of the magnetic field produced by a current-carrying circular loop. Mark on it the direction of (i) current and (ii) magnetic field lines. Name the two factors on which the magnitude of the magnetic field due to a current-carrying coil depends.
Explain the statement "Potential difference between two points is 1 volt".
What do the symbols given below represent in an electric circuit? Write one function of each.
Symbol of an Ammeter
What is asexual reproduction? Explain the process of budding in Hydra.
Why can't two magnetic field lines cross each other? Draw magnetic field lines showing the direction of the magnetic field due to a current-carrying long straight solenoid. State the conclusion which can be drawn from the pattern of magnetic field lines inside the solenoid. Name any two factors on which the magnitude of the magnetic field due to this solenoid depends.
A person uses lenses of power -0.5 D in his spectacles for the correction of his vision. (a) Name the defect of vision the person is suffering from.
Write chemical equations to show what happens when an acid reacts with a:
Write chemical equations to show what happens when an acid reacts with a:
(i) Metal
(ii) Base
(iii) Carbonate
Write the name of the main product formed in each case
Name the blood vessel that brings (i) oxygenated blood (ii) deoxygenated blood to the human heart. Also name that chamber of the heart which receives deoxygenated blood and state how deoxygenated blood from this chamber is sent to lungs for oxygenation.
"In human beings the genes inherited from the parents decide whether the newborn individual is male or female." Explain this statement with the help of a flow diagram.