List of top Science Questions asked in CBSE Class X

Absolute refractive indices of water and glass are $\frac{4}{3}$ and $\frac{3}{2}$ respectively. In which one of the two media is the speed of light more?

The absolute refractive indices of water and glass are $\frac{4}{3}$ and $\frac{3}{2}$ respectively. If the speed of light in glass is $2 \times 10^8$ m/s, find the speed of light in (i) water and (ii) vacuum.
“A ray of light incident on a rectangular glass slab immersed in any medium emerges parallel to itself.” Draw a labelled ray diagram to justify this statement.
Define the term absolute refractive index of a medium.
If a ray of light enters obliquely from glass to water, will it bend towards the normal or away from the normal?
Why is aluminium used to join railway tracks or the cracked machine parts of ‘iron’? Write a balanced chemical equation for the reaction which occurs.
How is the brain protected from shocks and injuries?
Write the main functions of (i) sensory neuron and (ii) motor neuron in a reflex arc.
Which part of the brain is involved in activities like (i) picking a pencil and (ii) vomiting? State whether these actions are voluntary or involuntary.
How does the central nervous system communicate with other parts of the body to carry out various activities? Name two components of this system.
Where is iron placed in the reactivity series of metals? Write the form/forms in which its ores are found in nature.
The commercial unit of electric energy is commonly known as ‘unit’. Write its actual name and establish the relationship between this unit and the SI unit of energy.
Define trophic levels. At which trophic level do we find (i) secondary and (ii) tertiary consumers in a food chain? What will happen if all the organisms of a trophic level die? Give reasons to justify your answer.
Name the parts in the human female reproductive system where the following functions take place:
(1) Maturation of eggs
(2) Fusion of the egg and the sperm
(3) Implantation of the zygote

Name the labelled parts A, B, C and D in the diagram given below.

Define water of crystallisation.
What is Tyndall effect? Give two examples where this phenomenon is observed. Give reason to explain this phenomenon.
An organic compound ‘X’ when reacts with sodium liberates hydrogen. The same compound ‘X’ when heated at 443 K in the presence of concentrated sulphuric acid gives an unsaturated hydrocarbon.
(i) Identify ‘X’.
Why are carbon compounds exceptionally stable?
With the help of a labelled circuit diagram, illustrate the pattern of the magnetic field lines of the magnetic field produced around a straight current carrying conductor. Explain how, with the help of right-hand thumb rule, we can determine and mark the direction of magnetic field lines due to a current.
What is photosynthesis? Name the organelle and the organs in which photosynthesis takes place. Where does the oxygen liberated come from during this process? What happens to the carbohydrates which are not immediately used by the plant?
Give the structure and function of alveoli in human respiratory system.
What is meant by residual volume of air in the lungs?
Write any two ways by which plants obtain carbon dioxide. What causes the opening and closing of the stomata?

Find the magnification of the image formed by a spherical mirror from the following data :
$u = -20$ cm,  $f = -15$ cm.