List of top Science Questions asked in CBSE X

How will the image formed by a convex lens be affected, if the upper half of the lens is wrapped with a black paper?

A uniform magnetic field exists in the plane of paper as shown in the diagram. In this field, an electron (e⁻) and a positron (p⁺) enter as shown. The electron and positron experience forces :

Which one of the following is not a natural ecosystem?

The phenomena of light involved in the formation of a rainbow are:

Sense organ in which olfactory receptors are present is:

A metal ‘X’ is used in the thermite process. When ‘X’ is heated with oxygen, it gives an oxide ‘Y’, which is amphoteric in nature. ‘X’ and ‘Y’ respectively are:

An aqueous solution of sodium chloride is prepared in distilled water. The pH of this solution is:

The correct sequence of events when someone’s hand touches a hot object (reflex action):

To balance the chemical equation, the values of the coefficients x, y, z, and t must be: Zn(NO₃)₂ → ZnO + NO₂ + O₂

The process in which transport of soluble products of photosynthesis takes place in plants is known as:

Which of the following is a redox reaction, but not a combination reaction?

An aqueous solution ‘A’ turns phenolphthalein solution pink. When another aqueous solution ‘B’ is added to the pink solution, the pink color disappears. Adding a few drops of solution ‘A’ again restores the pink color. The respective changes in the nature of the solution are:

The incorrect statement about placenta is: (A) It is a disc embedded in the uterine wall. (B) It connects the embryo to the side of the uterus. (C) It has a very small surface area for glucose and oxygen to pass from mother to embryo. (D) It secretes hormones for maintaining pregnancy.

Select from the following the conditions responsible for the rapid spread of black mould on a slice of bread: (i) Formation of large number of spores (ii) Presence of moisture and nutrients in bread (iii) Low temperature (iv) Presence of hyphae

Study the data given below showing the focal length of three concave mirrors A, B and C and the respective distances of objects placed in front of the mirrors:

Case	Mirror	Focal Length (cm)	Object Distance (cm)
1	A	20	45
2	B	15	30
3	C	30	20

(i) In which one of the above cases the mirror will form a diminished image of the object? Justify your answer.
(ii) List two properties of the image formed in case 2.
(iii) (A) What is the nature and size of the image formed by mirror C? Draw ray diagram to justify your answer.

OR

(iii) (B) An object is placed at a distance of 18 cm from the pole of a concave mirror of focal length 12 cm. Find the position of the image formed in this case.

(a) (i) Distinguish between hormonal co-ordination in plants and animals.
(ii) Which part of the brain is responsible for –
(1) intelligence
(2) riding a bicycle
(3) vomiting
(4) controlling hunger
(iii) How is brain and spinal-cord protected against mechanical injuries?
OR
(b) (i) What are tropic movements? Give an example of a plant hormone which (1) inhibits growth and (2) promotes cell division.
(ii) Explain directional movement of a tendril in pea plant in response to touch. Name the hormone responsible for this movement.

Salts play a very important role in our daily life. Sodium chloride which is known as common salt is used almost in every kitchen. Baking soda is also a salt used in faster cooking as well as in baking industry. The family of salts is classified on the basis of cations and anions present in them.
(a) Identify the acid and base from which Sodium chloride is formed.
(b) Find the cation and the anion present in Calcium sulphate.
(c) “Sodium chloride and washing soda both belong to the same family of salts.” Justify this statement.
OR
(c) Define the term pH scale. Name the salt obtained by the reaction of Potassium hydroxide and Sulphuric acid and give the pH value of its aqueous solution.

Give reasons for the following:
(i) Alveoli in lungs are richly supplied with blood capillaries.
(ii) Respiratory pigment in the blood takes up oxygen and not carbon dioxide.
(iii) During anaerobic respiration, a 3-carbon molecule is formed as an end product instead of CO₂ in human beings.
OR
(i) Name the movements that occur all along the gut in human digestive system. How do they help in digestion?
(ii) Where is bile juice stored in human body? List two roles of bile juice.

Draw a labelled diagram to show electrolytic refining of copper. State what happens when electric current is passed through the electrolyte taken in this case.

Study the I-V graph for three resistors of resistances R₁, R₂ and R₃ and select the correct statement from the following:

Asexual reproduction involves a single parent to produce offspring without the formation of gametes. It occurs by the following ways: Fission, Budding, Fragmentation, Spore formation and Regeneration. In one of the methods like regeneration, Planaria A is cut horizontally into three pieces – L, M and N and Planaria B is cut vertically into two equal halves – O and P.

(a) Which of the cut pieces of the two Planaria could regenerate to form a complete organism?
(b) Give an example of another organism which follows the same mode of reproduction as Planaria.
(c) What is the meaning of ‘development’ in regeneration?
OR
(c) Differentiate between regeneration and fragmentation.

When electric current flows in a purely resistive circuit electrical energy gets fully converted into heat energy. The amount of heat produced (H) in the circuit is found to be directly proportional to (i) the square of current (I²)
(ii) the resistance (R) of the conductor and
(iii) the time (t) for which current flows. In other words H = I²Rt. Electrical devices such an electric fuse, electric heater, electric iron etc. are all based on this effect called heating effect of electric current.
&
a) List two properties of heating elements.
b) List two properties of electric fuse.
c) Name the principle on which an electric fuse works. Explain how a fuse wire is capable of saving electrical appliances from getting damaged due to accidentally produced high currents.
OR
c) The power of an electric heater is 1100 W. If the potential difference between the two terminals of the heater is 220 V, find the current flowing in the circuit. What will happen to an electric fuse of rating 5 A connected in this circuit?

(a) Define the term power of accommodation of human eye. Write the name of the part of eye which plays a major role in the process of accommodation and explain what happens when human eye focuses (i) nearby objects and (ii) distant objects.
OR
(b) Draw a ray diagram to show the formation of a rainbow in the sky. On this diagram mark A – where dispersion of light occurs, B – where internal reflection of light occurs and C – where refraction of light occurs. List two necessary conditions to observe a rainbow.

(a) Upper half of a convex lens is covered with a black paper. Draw a ray diagram to show the formation of image of an object placed at a distance of 2F from such a lens. Mention the position and nature of the image formed. State the observable difference in the image obtained if the lens is uncovered. Give reason to justify your answer.
(b) An object is placed at a distance of 30 cm from the optical centre of a concave lens of focal length 15 cm. Use lens formula to determine the distance of the image from the optical centre of the lens.

It is observed that Calcium on reaction with water floats on its surface. Explain why it happens. Also write a balanced chemical equation for the reaction that occurs. What happens when the aqueous solution of the product of this reaction reacts with Carbon dioxide gas? Write a balanced chemical equation for the reaction.