List of top Science Questions asked in CBSE X

The oxide which can react with HCl as well as KOH to give corresponding salt and water is

Solid Calcium oxide reacts vigorously with water to form Calcium hydroxide accompanied by the liberation of heat. From the information given above it may be concluded that this reaction

Select from the following a process in which a combination reaction is involved:

(A) (i) Define electric power. Express it in terms of potential difference (V) and resistance (R).
(ii) An electric oven is designed to work on the mains voltage of 220 V. This oven consumes 11 units of electrical energy in 5 hours. Calculate:
(a) power rating of the oven
(b) current drawn by the oven
(c) resistance of the oven when it is red hot

OR

(B) (i) Write the relation between resistance R and electrical resistivity ρ of the material of a conductor in the shape of a cylinder of length 𝑙 and area of cross-section A. Hence derive the SI unit of electrical resistivity.
(ii) The resistance of a metal wire of length 3 m is 60 Ω. If the area of cross-section of the wire is \(4 \times 10^{-7}\) m², calculate the electrical resistivity of the wire.
(iii) State how would electrical resistivity be affected if the wire (of part ‘ii’) is stretched so that its length is doubled. Justify your answer.

Mendel worked out the rules of heredity by working on garden pea using a number of visible contrasting characters. He conducted several experiments by making a cross with one or two pairs of contrasting characters of pea plant. On the basis of his observations he gave some interpretations which helped to study the mechanism of inheritance.
(i) When Mendel crossed pea plants with pure tall and pure short characteristics to produce F₁ progeny, which two observations were made by him in F₁ plants?
(ii) Write one difference between dominant and recessive trait.
(iii) (A) In a cross with two pairs of contrasting characters
                   RRYY × rryy
      (Round Yellow)   (Wrinkled Green)
Mendel observed 4 types of combinations in F₂ generation. By which method did he obtain F₂ generation? Write the ratio of the parental combinations obtained and what conclusions were drawn from this experiment.

OR

(iii) (B) Justify the statement :
“It is possible that a trait is inherited but may not be expressed.”

The metals produced by various reduction processes are not very pure. They contain impurities, which must be removed to obtain pure metals. The most widely used method for refining impure metals is electrolytic refining.
(i) What is the cathode and anode made of in the refining of copper by this process?
(ii) Name the solution used in the above process and write its formula.
(iii) (A) How copper gets refined when electric current is passed in the electrolytic cell?
OR
(iii) (B) You have two beakers ‘A’ and ‘B’ containing copper sulphate solution. What would you observe after about 2 hours if you dip a strip of zinc in beaker ‘A’ and a strip of silver in beaker ‘B’? Give reason for your observations in each case.

Juice of tamarind turns blue litmus to red. It is because of the presence of an acid called:

(i) Why is respiratory pigment needed in multicellular organisms with large body size?
(ii) Give reasons for the following:
(a) Rings of cartilage are present in the throat.
(b) Lungs always contain a residual volume of air.
(c) The diaphragm flattens and ribs are lifted up when we breathe in.
(d) Walls of alveoli contain an extensive network of blood vessels.

(A) (i) Name three techniques/devices used by human females to avoid pregnancy. Mention the side effects caused by each.
(ii) What will happen if in a human female (a) fertilisation takes place, (b) an egg is not fertilised?

OR

(B) (i) Draw a diagram showing spore formation in Rhizopus and label the (a) reproductive and (b) non-reproductive parts. Why does Rhizopus not multiply on a dry slice of bread?
(ii) Name and explain the process by which reproduction takes place in Hydra.

(A) Plants → Deer → Lion
In the given food chain, what will be the impact of removing all the organisms of second trophic level on the first and third trophic level?
Will the impact be the same for the organisms of the third trophic level in the above food chain if they were present in a food web? Justify.
OR
(B) A gas ‘X’ which is a deadly poison is found at the higher levels of atmosphere and performs an essential function.
Name the gas and write the function performed by this gas in the atmosphere. Which chemical is linked to the decrease in the level of this gas? What measures have been taken by an international organization to check the depletion of the layer containing this gas?

Define reflex action. With the help of a flow chart show the path of a reflex action such as sneezing.

Name and state the rule to determine the direction of a:
(i) magnetic field produced around a current carrying straight conductor.
(ii) force experienced by a current carrying straight conductor placed in a magnetic field which is perpendicular to it.

(i) The pH of a sample of tomato juice is 4.6. How is this juice likely to be in taste? Give reason to justify your answer.
(ii) How do we differentiate between a strong acid and a weak base in terms of ion-formation in aqueous solutions?
(iii) The acid rain can make the survival of aquatic animals difficult. How?

(A) (i) Define a homologous series of carbon compounds.
(ii) Why is the melting and boiling points of \(C_4H_8\) higher than that of \(C_3H_6\) or \(C_2H_4\)?
(iii) Why do we NOT see any gradation in chemical properties of a homologous series compounds?
(iv) Write the name and structures of (i) aldehyde and (ii) ketone with molecular formula \(C_3H_6O\).

OR

(B) (i) Write the name and structure of an organic compound ‘X’ having two carbon atoms in its molecule and its name is suffixed with ‘-ol’.
(ii) What happens when ‘X’ is heated with excess concentrated sulphuric acid at 443 K? Write chemical equation for the reaction stating the conditions for the reaction. Also state the role played by concentrated sulphuric acid in the reaction.
(iii) Name and draw the electron dot structure of hydrocarbon produced in the above reaction.

Study the diagram given below and answer the questions that follow:

(i) Name the defect of vision represented in the diagram. Give reason for your answer.
(ii) List two causes of this defect.
(iii) With the help of a diagram show how this defect of vision is corrected.

Name the type of chemical reaction in which calcium oxide reacts with water. Justify your answer by giving balanced chemical equation for the chemical reaction.

Write one chemical equation each for the chemical reaction in which the following have taken place:
(i) Change in colour
(ii) Change in temperature
(iii) Formation of precipitate
Mention colour change/temperature change (rise/fall)/compound precipitated along with equation.

(A)Show how you would connect three resistors each of resistance 6 $\Omega$, so that the combination has a resistance of 9 $\Omega$. Also justify your answer.
OR
(B)In the given circuit, calculate the power consumed in watts in the resistor of 2 $\Omega$.

(A) How is the movement of leaves of a sensitive plant different from the downward movement of the roots ?
OR
(B) There is a hormone which regulates carbohydrate, protein and fat metabolism in our body. Name the hormone and the gland which secretes it. Why is it important for us to have iodised salt in our diet?

(i) Two magnetic field lines do not intersect each other. Why?
(ii) How is a uniform magnetic field in a given region represented?
Draw a diagram in support of your answer.

State one role of each of the following in human digestive system :
(i) Hydrochloric acid
(ii) Villi
(iii) Anal Sphincter
(iv) Lipase

An object is placed at a distance of 10 cm from a convex mirror of focal length 15 cm. Find the position of the image formed by the mirror.

Assertion (A): The rainbow is a natural spectrum of sunlight in the sky.
Reason (R) : Rainbow is formed in the sky when the sun is overhead and water droplets are also present in air.

Assertion (A) : Hydrogen gas is not evolved when zinc reacts with nitric acid.
Reason (R) : Nitric acid oxidises the hydrogen gas produced to water and itself gets reduced.

In which of the following organisms, multiple fission is a means of asexual reproduction ?