List of top Questions asked in CBSE Class X

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.
MnO2 + 4HCl → MnCl2 + 2H2O + Cl2
The reaction given above is a redox reaction because in this case:
At what distance from a convex lens should an object be placed to get an image of the same size as that of the object on a screen ?
A stomata closes when :
(i) it needs carbon dioxide for photosynthesis.
(ii) it does not need carbon dioxide for photosynthesis.
(iii) water flows out of the guard cells.
(iv) water flows into the guard cells.
The correct reason(s) in this process is/are :
Chromosomes:
(i) carry hereditary information from parents to the next generation.
(ii) are thread like structures located inside the nucleus of an animal cell.
(iii) always exist in pairs in human reproductive cells.
(iv) are involved in the process of cell division.
The correct statements are:
The lens system of human eye forms an image on a light sensitive screen, which is called as :
Consider the following statements:
(i) The sex of a child is determined by what it inherits from the mother.
(ii) The sex of a child is determined by what it inherits from the father.
(iii) The probability of having a male child is more than that of a female child.
(iv) The sex of a child is determined at the time of fertilisation when male and female gametes fuse to form a zygote.
The correct statements are:
In a nerve cell, the site where the electrical impulse is transmitted to the next neuron is called:
Oxides of aluminium and zinc are :
Carbon compounds :
(i) are good conductors of electricity.
(ii) are bad conductors of electricity.
(iii) have strong forces of attraction between their molecules.
(iv) have weak forces of attraction between their molecules.
The correct statements are :
Select from the following a decomposition reaction in which the source of energy for decomposition is light:
Consider the following compounds:
FeSO4 ; CuSO4 ; CaSO4 ; Na2CO3
The compound having the maximum number of water of crystallisation in its crystalline form in one molecule is:
A metal and a non-metal that exists in liquid state at the room temperature are respectively :
When 2 mL of sodium hydroxide solution is added to a few pieces of granulated zinc in a test tube and then warmed, the reaction that occurs can be written in the form of a balanced chemical equation as:
Explain the following in terms of gain or loss of oxygen with two examples each. 
(a) Oxidation
(b) Reduction
Write the balanced chemical equations for the following reactions. 
(a) Calcium hydroxide + Carbon dioxide \(→\) Calcium carbonate + Water 
(b) Zinc + Silver nitrate \(→\) Zinc nitrate + Silver 
(c) Aluminium + Copper chloride \(→\) Aluminium chloride + Copper 
(d) Barium chloride + Potassium sulphate \(→\) Barium sulphate + Potassium chloride
How did Mandela’s understanding of freedom change with age and experience?
A ladder has rungs 25 cm apart. (see Fig. 5.7). The rungs decrease uniformly in length from 45 cm at the bottom to 25 cm at the top. If the top and the bottom rungs are \(2\frac 12\) m apart, what is the length of the wood required for the rungs?
A ladder has rungs 25 cm apart.
Fig. 5.7

In a retail market, fruit vendors were selling mangoes kept in packing boxes. These boxes contained varying number of mangoes. The following was the distribution of mangoes according to the number of boxes.

Number of heartbeats per minute50-5253-5556-5859-6162-64
Number of boxs1511013511525

Find the mean number of mangoes kept in a packing box. Which method of finding the mean did you choose?

The table below shows the daily expenditure on food of 25 households in a locality

Daily expenditure  (in Rs)100 - 150150 - 200 200 - 250 250 - 300300 - 350
Number of households451222

Find the mean daily expenditure on food by a suitable method.

The angle of elevation of the top of a building from the foot of the tower is 30° and the angle of elevation of the top of the tower from the foot of the building is 60°. If the tower is 50 m high, find the height of the building.
Light enters from air to glass having refractive index 1.50. What is the speed of light in the glass? The speed of light in vacuum is 3 × 108 m s−1.
This episode describes the silly behaviour of a rich woman who is foolishly indulgent, perhaps because she is lonely. Do you think such people are merely silly, or can their actions cause harm to others?
What are some of the things you now know about
(i) The people of Coorg?
(ii) The main crop of Coorg?
(iii) The sports it offers to tourists?
(iv) The animals you are likely to see in Coorg?
(v) Its distance from Bangalore, and how to get there?
Was Anne right when she said that the world would not be interested in the musings of a thirteen-year-old girl?