List of top Science Questions asked in CBSE Class X

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

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

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

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

Consider the following cases:
(a) CaSO₄ + Al →
(b) CuSO₄ + Ca →
(c) FeSO₄ + Cu →
(d) ZnSO₄ + Mg →
The cases in which new products will form are –

Identify the correct statement about the following reaction:
2H₂S + SO₂ → 2H₂O + S

Consider the following statements about homologous series of carbon compounds:
(a) All succeeding members differ by –CH₂ unit.
(b) Melting point and boiling point increases with increasing molecular mass.
(c) The difference in molecular masses between two successive members is 16 u.
(d) C₂H₂ and C₃H₄ are NOT the successive members of alkyne series.
The correct statements are –

Which of the following statement(s) is (are) true about human heart?
(a) Right atrium receives oxygenated blood from lungs through pulmonary artery.
(b) Left atrium transfers oxygenated blood to left ventricle which sends it to various parts of the body.
(c) Right atrium receives deoxygenated blood through vena cava from upper and lower body.
(d) Left atrium transfers oxygenated blood to aorta which sends it to different parts of the body.

Select out of the following a gland which does NOT occur as a pair in the human body:

In human respiratory system, when a person breathes in, the position of ribs and diaphragm will be:

Identify the mode of asexual reproduction in the following organism:

A cross made between two pea plants produces 50% tall and 50% short pea plants. The gene combination of the parental pea plants must be

Consider the following statements in the context of human eye:
(a) The diameter of the eye ball is about 2.3 cm.
(b) Iris is a dark muscular diaphragm that controls the size of the pupil.
(c) Most of the refraction for the light rays entering the eye occurs at the crystalline lens.
(d) While focusing on the objects at different distances the distance between the crystalline lens and the retina is adjusted by ciliary muscles.
The correct statements are –

The maximum resistance of a network of five identical resistors of $\frac{1}{5}$ $\Omega$ each can be –

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

Strength of magnetic field produced by a current carrying solenoid DOES NOT depend upon:

Assertion (A): Different metals have different reactivities with water and dilute acids.
Reason (R): Extraction of a metal from its ore depends on its position in the reactivity series.

Assertion (A): Human female has a perfect pair of sex chromosomes.
Reason (R): Sex chromosome contributed by the human male in the zygote decides the sex of a child.

Assertion (A): Myopic eye cannot see distant objects distinctly.
Reason (R): For the correction of myopia converging lenses of appropriate power are prescribed by eye-surgeons.

Assertion (A): The deflection of a compass needle placed near a current carrying wire decreases when the magnitude of an electric current in the wire is increased.
Reason (R): Strength of the magnetic field at a point due to a current carrying conductor increases on increasing the current in the conductor.

(a) “No precipitation reaction can occur without exchange of ions between the two reactants.” Justify this statement giving a balanced chemical equation for the reaction.
OR
(b) Giving one example of each, differentiate between a displacement reaction and a double displacement reaction.

Photosynthesis takes place in the leaves and the food prepared by it reaches other parts of the plants. Name the process involved and explain it.

“Stability of DNA in a species is ensured during sexual reproduction.” Justify the statement.

(a) State two laws of refraction of light.
(b) Define the term absolute refractive index of a medium. A ray of light enters from vacuum to glass of absolute refractive index 1.5. Find the speed of light in glass. The speed of light in vacuum is \(3 \times 10^8\) m/s.

Use Ohm’s law to determine the potential difference across the 3 \(\Omega\) resistor in the circuit shown in the following diagram when key is closed: