List of top Science Questions asked in CBSE Class X

Explain the mechanism of inheritance used by sexually reproducing organisms to ensure the stability of DNA of the species. 

Identify from the following the ray diagram which shows the correct path of the reflected ray for the ray incident on a concave mirror as shown:
path of the reflected ray for the ray incident on a concave mirror
The water of crystallization is present in:
(i) Bleaching Powder
(ii) Plaster of Paris
(iii) Washing Soda
(iv) Baking Soda
In a bisexual flower the male gametes are present in the :
Write chemical equations to show what happens when an acid reacts with a:
Write chemical equations to show what happens when an acid reacts with a:
(i) Metal
(ii) Base
(iii) Carbonate
Write the name of the main product formed in each case
Give two methods used to grow rose and jasmine plants by vegetative propagation.
Define a precipitation reaction. Give its example and also express the reaction that occurs in the form of a balanced chemical equation.
A tall pea plant with round seeds (TTRR) is crossed with a short pea plant with wrinkled seeds (ttrr). The \( F_1 \) generation will be:
The basic filtration unit of the excretory system in human beings is:
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 human alimentary canal, the digestive juice secreted by the gastric glands are:
Assertion (A) : In large animals, oxygen can reach different parts of the animal's body easily.
Reason (R) : Respiratory pigments take up oxygen from the air and carry it to body tissues.
Which one of the following is not an excretory product in plants?
Juice of tamarind turns blue litmus to red. It is because of the presence of a chemical compound called:
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:
Example of thermal decomposition reaction are:
  1. \( \text{2AgCl} \rightarrow \text{2Ag} + \text{Cl}_2 \)
  2. \( \text{CaCO}_3 \rightarrow \text{CaO} + \text{CO}_2 \)
  3. \( \text{2H}_2\text{O} \rightarrow \text{2H}_2 + \text{O}_2 \)
  4. \( \text{2KClO}_3 \rightarrow \text{2KCl} + \text{3O}_2 \)

Select from the following a statement which is not true about the burning of magnesium ribbon in air:

The colour of the solution observed after about 1 hour of placing iron nails in copper sulphate solution is: 

In which one of the following situations a chemical reaction does not occur?
In order to prepare dry hydrogen chloride gas in a humid atmosphere, the gas produced is passed through a guard tube (drying tube) which contains:

The basic filtration unit of the excretory system in human beings is:

Assertion (A): Carbon and its compounds are our major sources of fuels. 
Reason (R): Most of the carbon compounds on burning release a large amount of heat and light.

You have three aqueous solutions A, B, and C as given below: 
A - Potassium nitrate 
B - Ammonium chloride 
C - Sodium carbonate 
The ascending order of the pH of these solutions is:

Select the option having correct matching of the organism given in Column I with the mode of reproduction in Column II: Column I {0.2cm}

A hydrocarbon which does not belong to the same homologous series of carbon compounds is