List of top Science Questions asked in CBSE Class X

In the food chains given below, select the most efficient food chain in terms of energy:
The minimum number of identical bulbs of rating 4V, 6W, that can work safely with desired brightness, when connected in series with a 240V mains supply is:
Out of the two media - Medium 1 and Medium 2, in which is the speed of light more?
path of a ray of light going from Medium 1 to Medium 2
Show the formation of magnesium chloride by electron transfer. Write the name of the cation and anion present in the compound formed. (Atomic Number of Mg = 12, Cl = 17)
Why do we balance a chemical equation? Name and state the law that suggests the balancing of a chemical equation. Balance the following chemical equation: \[ {Zn} + {H}_3 {PO}_4 \rightarrow {Zn}_3 {(PO}_4{)}_2 + {H}_2 \]
Write one function each of the parts - (i) petals (ii) anther (iii) style and (iv) ovary of a bisexual flower.

(i) Study the diagram and name the parts marked as A, B, C, and D. 
(ii) Write the function of A and C.

 

Name the method by which Amoeba and Leishmania reproduce. Write a major difference in the way they divide to produce new individuals.
Consider the following food chain:
Grass \( \rightarrow \) Grasshopper \( \rightarrow \) Frog \( \rightarrow \) Snake \( \rightarrow \) Eagle
If the amount of energy available at third trophic level is 50 kJ, the available energy at the producer level was:
In our houses we receive A.C. electric power of 220 V. In electric iron or electric heater cables having three wires with insulation of three different colours – red, black and green are used to draw current from the mains. What are these three different wires called? Name them colourwise. What is the potential difference between the red wire and the black wire? What is the role of the wire with green insulation in case of accidental leakage of electric current to the metallic body of an electrical appliance?
Which one of the following gets biomagnified at different levels in a food chain?
When will the magnitude of the force be highest?
Name the type of lenses required by the persons for the correction of their defect of vision called presbyopia. Write the structure of the lenses commonly used for the correction of this defect giving reason for such designs.
"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.
Explain why respiration is considered an exothermic reaction. Give the chemical equation for this reaction.
What is a rainbow? 'We see a rainbow in the sky only after the rainfall.' Why?
The sky appears dark to passengers flying at very high altitude
Name a metal found in the earth's crust:
(i) in free state and
(ii) in the form of its compound.
State where each of these metals are placed in the reactivity series of metals

Leaves of the sensitive plant move very quickly in response to ‘touch’. How is this stimulus of touch communicated and explain how the movement takes place? 

Assertion (A): Concentrated nitric acid is diluted by adding water slowly to acid with constant stirring.
Reason (R): Concentrated nitric acid is easily soluble in water.
In the light of the above statements, choose the most appropriate answer from the options given below:

We do not clean natural ponds or lakes, whereas an aquarium or a swimming pool needs to be cleaned regularly. Why? 

What happens when butane is burnt in air? Write the chemical equation for the reaction. Differentiate between the flames obtained when butane and butyne both are burnt in air in similar conditions.
Explain the mechanism of inheritance used by sexually reproducing organisms to ensure the stability of DNA of the species.

Draw the pattern of the magnetic field lines for the two parallel straight conductors carrying current of same magnitude 'I' in opposite directions as shown. Show the direction of magnetic field at a point O which is equidistant from the two conductors. (Consider that the conductors are inserted normal to the plane of a rectangular cardboard.)

 

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.