List of top Science Questions asked in CBSE X

Identify the food chain in which the organisms of the second trophic level are missing :
Assertion (A): Accumulation of harmful chemicals is maximum in the organisms at the highest trophic level of a food chain.
Reason (R) : Harmful chemicals are sprayed on the crops to protect them from diseases and pests.
Assertion (A): The rate of breathing in aquatic organisms is much faster than in terrestrial organisms.
Reason (R) :The amount of oxygen dissolved in water is very high as compared to the amount of oxygen in air.
The pattern of the magnetic field produced inside a current carrying solenoid is :
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 :
In a nerve cell, the site where the electrical impulse is transmitted to the next neuron is called:
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:
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:
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 ?
MnO2 + 4HCl → MnCl2 + 2H2O + Cl2
The reaction given above is a redox reaction because in this case:
The lens system of human eye forms an image on a light sensitive screen, which is called as :
A metal and a non-metal that exists in liquid state at the room temperature are respectively :
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:
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:
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:
Show how you would connect three resistors, each of resistance 6 Ω, so that the combination has a resistance of 
  1. 9 Ω
  2. 4 Ω
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
Draw the structure of a neuron and explain its function.
Explain the following terms with one example each. 
(a) Corrosion 
(b) Rancidity
A battery of 9 V is connected in series with resistors of 0.2 Ω, 0.3 Ω, 0.4 Ω , 0.5 Ω and 12 Ω, respectively. How much current would flow through the 12 Ω resistor?
Balance the following chemical equations.
(a) HNO3 +Ca(OH)2 \(→\) Ca(NO3)2 + H2O 
(b) NaOH + H2SO4 \(→\) Na2SO4 + H2O 
(c) NaCl + AgNO3 \(→\) AgCl + NaNO3 
(d) BaCl + H2 SO4 \(→\) BaSO4 + HCl
Explain the following in terms of gain or loss of oxygen with two examples each. 
(a) Oxidation
(b) Reduction
Oil and fat containing food items are flushed with nitrogen. Why?