List of top Science Questions asked in CBSE Class X

Which of the following group is not ‘biodegradable’ ?

Sex is determined by different factors in various species. However, in human beings, it is determined genetically. Which amongst the following option(s) is/are correct for human beings ?
Gamete carrying X chromosome from female parent.
Gamete carrying X chromosome from male parent.
Gamete carrying Y chromosome from male parent.

Human brain has various parts or regions that help in different actions, responses and coordination. From the following, identify the part responsible for precision of voluntary actions :

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?

The pattern of magnetic field due to a current carrying wire depends upon the shape made by that wire. Justify.

(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.

What happens when : (a) An iron nail is dipped in copper (II) sulphate solution ?
(b) Potassium iodide solution is mixed with lead nitrate solution ?
(c) Silver chloride is exposed to sunlight ?
Write balanced chemical equations to support your answer.

Why does one feels pain and irritation when stung by honey-bee?
Rubbing of baking soda on the stung area gives relief. How?

Assertion (A): Carbon shares its valence electrons with other atoms of carbon or with atoms of other elements.
Reason (R): The shared electrons belong to the outermost shells of both the atoms and lead to both atoms attaining the noble gas configuration.

The natural sources of oxalic acid, lactic acid and methanoic acid respectively are:

Which of the following is a poor conductor of electricity?

When an element 'X' reacts with water, it starts floating. Identify the element 'X':

The hydrocarbons with general formula \( C_nH_{2n} \) represents: