List of top Science Questions asked in CBSE Class X

Define the S.I. unit of electric current.
Conductors of electric toasters and electric iron are made of an alloy rather than a pure metal. Why ?
Due to change in length and area of cross-section of a conductor, resistance of conductor changes while resistivity does not change. Why ?
A person is unable to read a book placed closer than \( 1 \text{ meter} \) from his eyes. Identify the defect of vision in his eyes. Draw the ray diagrams to show the defect of vision and its correction.
Write the preparation of following compounds with balanced chemical equation :
Baking soda
Bleaching powder
Plaster of Paris
Explain chlor-alkali process with chemical equation. Name the products formed at anode and cathode.
Give one example each of electrolytic decomposition and decomposition by sunlight.
Balance the following chemical reaction: \( Pb(NO_3)_2 + KI \longrightarrow PbI_2 + KNO_3 \)
Name the substance oxidised and reduced in the following reaction: \( ZnO + C \longrightarrow Zn + CO \)
Categorise the following based on their nature: \( ZnO, Na_2O, CO_2 \)
What are amphoteric oxides?
Which of the following group is not ‘biodegradable’ ?
Derive the expression for the equivalent resistance of three resistors \( R_1 \), \( R_2 \) and \( R_3 \) connected in parallel combination.
Two lamps 'A' and 'B' of rating 50 W; 220 V and 100 W, 220 V are connected in series combination. Find out the ratio of the resistances (\(R_A : R_B\)) of these lamps.
(a) What is hypermetropia?
(b) Write any one cause of hypermetropia.
(c) With the help of a suitable ray diagram, explain how hypermetropia is corrected?
Describe an activity to show that a current carrying conductor, placed in an external magnetic field experiences a force.
A current carrying straight wire AB is shown in the given diagram. Out of X, Y and Z on which point will the strength of magnetic field be maximum and why?
(a) The resistance of a wire of 0.01 cm radius and 1.0 cm length is \( 7 \, \Omega \).
Calculate its resistivity.
OR
(b) An electric heater is rated 220 V; 11 A. Calculate the power consumed if the heater is operated at 200 V.
Assertion (A): When rays of white light pass through a prism, on emerging they give spectrum of seven colours.
Reason (R): It is due to the scattering of light that red light bends minimum and violet light bends the maximum.
When you look at an object very close to your eyes, the:
A convex lens of focal length 15 cm, is forming a real image. If the size of image is same as the size of object, then position of object and position of image will be, respectively :
Mohan heated ethanol with a compound 'X' in the presence of a few drops of conc. \( H_2SO_4 \) and observed a sweet smelling compound 'Y' is formed. When 'Y' is treated with sodium hydroxide it gives back ethanol and a compound 'Z'.
(i) Identify 'X', 'Y' and 'Z'.
(ii) Write the role of conc. \( H_2SO_4 \) in the reaction.
(iii) Write the chemical equations involved and name the reactions.
Write chemical equations for the following :
(I) Oxidation of ethanol by acidified K₂Cr₂O₇.
(II) Hydrogenation of ethene.
Give reasons for the following:
(I) Covalent compounds are poor conductor of electricity.
(II) Soap does not form lather in hard water.
(III) Carbon shows catenation but silicon does not.
Explain chlor-alkali process with chemical equation. Name the products formed at anode and cathode.